beyond mendelian genetics in cases in which 2 or more … · 2020-02-04 · 2/4/20 1 beyond...

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BEYOND MENDELIAN GENETICS There are many variations of inheritance patterns.

A SUMMARY OF MENDEL’S PRINCIPLES

!  The inheritance of biological characteristics is determined by individual units known as genes, which are passed from parents to offspring.

!  In cases in which 2 or more alleles of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.

!  In most sexually reproducing organisms, each adult has 2 copies of each gene- one from each parent. These genes are segregated when gametes are formed.

!  The alleles for different genes usually segregate independently of one another.

BEYOND DOMINANT AND RECESSIVE ALLELES

!  There are exceptions to Mendel’s work !  Not all genes show simple patterns of dominant and recessive !  In most organisms, genetics is more complicated. !  Some alleles are neither dominant nor recessive, and many

traits are controlled by multiple alleles or multiple genes! !  Many genes have more than just 2 alleles

!  eye color: blue, brown, hazel, green, grey, gold…

INCOMPLETE DOMINANCE

o  Incomplete dominance one allele is not completely dominant over another; can result in blending of trait. o  The heterozygous trait is somewhere between

the homozygous traits

o  Example: Four o’clock plants o  Red Flowers: RR o  White Flowers:

WW o  A cross between

these gives 100% RW

o  Neither R nor W is dominant so the flowers are pink!

CODOMINANCE

o  Similar to incomplete dominance o  Codominance: occurs when both alleles

contribute to the phenotype; both traits appear. o  No blending

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CODOMINANCE EXAMPLE

o  Example: Erminette Chickens o  “looks speckled” o  Black (BB) feathers are

dominant over white (WW) feathers

o  When crossed the heterozygous (BW) chickens have both black and white feathers

CODOMINANCE EXAMPLES

INCOMPLETE DOMINANCE AND CODOMINANCE WORKSHEET

Chickens : Codominance

Snapdragons: Incomplete Dominance

DOMINANT OR RECESSIVE?

�� What makes an allele dominant, recessive or codominant? �� The nature of the gene’s PROTEIN and its role in

the cell!

MULTIPLE ALLELES

o  Multiple alleles: genes that have more than just 2 alleles. o  This does not mean that the

individual can have more than 2 alleles for a gene

o  Only means that there are more than only 2 outcomes in a POPULATION

Phenotype Possible Genotypes

BBEE BbEE BBEe BbEe

bbEE bbEe

BBee Bbee bbee

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o  Example: Rabbit coat color o  Controlled by a single gene that has 4 diff. alleles. o  Display simple pattern of inheritance o  4 different coat variations possible

o  Full color o  Chinchilla o  Himalayan o  Albino

DIHYBRID CROSS

o  Dihybrid cross: mating of two organisms that differ in two characters

LAW OF INDEPENDENT ASSORTMENT

o  Mendel’s second law was concluded after finding approximately a 9:3:3:1 phenotypic ratio in the F2 generation of pea plants.

o  He realized… o  One trait’s presence did not affect

the presence of another trait o  Law of independent assortment –

allele pairs separate independently of each other during gamete formation, or meiosis. o  Different traits are inherited

separately

TRY IT! LAW OF INDEPENDENT ASSORTMENT

!  In mice fur color is controlled by two separate genes on separate chromosomes. !  This means the sort independently. !  The alleles have a dominant/recessive interaction !  B=Black, b=brown AND E = long ears, e= short ears

1.  What is the genotype of a mouse with brown fur and short ears?

2.  What is the genotype of a mouse that is heterozygous for both traits? What is it phenotype?

3.  How many possible combinations of alleles could be found in the gamete of the mouse in #2?

WHAT DOES A DIHYBRID CROSS OF OUR MICE LOOK LIKE?

POLYGENIC TRAITS o  Polygenic traits: trait controlled by 2 or more genes o  Many genes could be contributing to the trait o  Skin color in humans varies so much because several

genes which each have several alleles contribute to it.

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SEX LINKED TRAITS (OR X-LINKED)

!  2000 genes on X vs. 100 on Y ! Many genes on X do NOT have a match on Y ! Examples in Humans:

!  Red-green color blindness !  Hemophilia !  Male Pattern Baldness !  Duchenne Muscular Dystrophy

TRY IT! SEX LINKED RED-GREEN COLOR BLINDNESS

! B = normal vision, b = color blindness 1.  What is the genotype of a female who is color

blind? What is the genotype of a male who is color blind?

2.  What is the genotype for a female who is a carrier? This mean she has the color blind allele but does not show the trait.

MODELING A SEX LINKED TRAIT ! Trait: Red-green color blindness ! X-linked recessive carried ONLY on X

chromosome Directions: 1.  On your white board, record the genotypes of

the parents you were given: XBXb x XBY OR XBXb x XbY OR XBXB x XbY

2.  Mom flips coin then dad flips coin 3.  Record the sex of the child AND if it is normal

or color blind. 4.  Repeat to get 10 data points 5.  Summarize the data- how many males color

blind and normal, how many females color blind or normal

6.  Record in class data on board

MODELING A SEX LINKED TRAIT !  Trait: Red-green color

blindness !  X-linked recessive carried

ONLY on X chromosome

Carrier Mom, Normal Dad XBXb x XBY

Male Female

Normal Vision Normal Vision

Color Blind Color Blind

Carrier Mom, Color Blind Dad

XBXb x XbY

Male Female



Normal Mom, Color Blind Dad

XBXB x XbY

Male Female



Deoxyribonucleic acid

DNA

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QUESTIONS MENDEL MAY HAVE ASKED…..

o  How do genes work? o  What are they made of? o  How do they determine characteristics of

organisms? o  Are they a single molecule structure or more

complex?

o  If the structures that carry genetic information could be identified, it might be possible to understand how genes control the inherited characteristics of living things.

OH WAIT…. WE DID THIS ALREADY!!!

THE DOUBLE HELIX

�� Remember ME????

GENES AND PROTEINS

o  Genes are coded DNA instructions that control the production of proteins within the cell.

o  Proteins create the traits!

THE GENETIC CODE

o  Proteins are made by joining amino acids into long chains called polypeptides.

o  4 base pairs carry instructions for 20 different amino acids. o  The genetic code is

read 3 letters at a time so that each “word” of the coded message is 3 bases long.

GENES AND PROTEINS

o  Genes contain nothing more than instructions for assembling proteins!

o  Remember, many proteins are enzymes, which catalyze (speed up) and regulate chemical reactions. o  Ex. A gene that

codes for an enzyme to produce pigment can control the color of a flower.

Meiosis explains Mendel’s Principles

CHROMOSOME THEORY OF INHERITANCE

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BIRTH OF THE CHROMOSOME THEORY OF INHERITANCE

o  Late 1800’s: Processes of mitosis & meiosis was worked out

o  1900’s: Researchers noticed parallels between the behavior of chromosomes and the behavior of Mendel's heritable factors (genes).

o  One of biology's most important theories—the chromosome theory of inheritance—emerged.

CHROMOSOME THEORY OF INHERITANCE

o  The chromosome theory of inheritance states that o  genes are located on

chromosomes

o  the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

o  Indeed, it is chromosomes that undergo segregation and independent assortment during meiosis and thus account for Mendel's two principles of the same name.

GENE LOCUS

��  Every diploid individual has two sets of homologous chromosomes. ��  One set from mom, the other set from dad

��  The alleles of a gene reside at the same location, called a gene locus (plural, loci), on homologous chromosomes

��  Homologous chromosomes may bear either the ��  same alleles at a particular locus- homozygous ��  different alleles at a particular locus-heterozygous

GENETIC LINKAGE AND CROSSING OVER

o  Gene Location o  Separate chromosomes

o  alleles sort independently of each other during meiosis

o  Same chromosome o  alleles for these genes would stay together

during meiosis o  The only way such alleles can sort

independently is if crossing over during meiosis separates them.

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GENETIC LINKAGE

o  the tendency for the alleles on one chromosome to be inherited together

o  closer two genes are on a chromosome, the greater the genetic linkage

AUTOSOME

SEX CHROMOSOME

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HUMAN HEREDITY

SEX DETERMINATION IN HUMANS

! The Y chromosome contains a male sex determining region that is responsible for male sexual development.

!  It determines male no matter how many X’s are present.

!  If the Y is absent however it will always develop female.

AUTOSOME

SEX CHROMOSOME

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SEX CELL SEGREGATION

o  As the punnet square shows you, males and females are born in a roughly 50:50 ratio

o  This is because of the way sex sex segregate during meiosis.

o  All human egg cells carry a single X chromosome (23,X)

o  However half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y).

o  This ensures that just about half of the zygotes will be 46,XX and half will be 46,XY

GENETIC COUNSELOR

o  When two people are considering having children, and one or both has a family history of a genetic disease, it may be helpful for the couple to visit a genetic counselor

o  genetic counselor: person trained to collect, analyze, and explain data about human inheritance patterns.

HUMAN TRAITS – PEDIGREE CHART

A pedigree chart shows the relationships within a family.

What doe the lines and shapes mean?? Fill in your diagram as we review.

HUMAN TRAITS - PEDIGREE CHART

o  Hemophilia is a sex-linked recessive trait

o  A pedigree will allow you to trace how a disease passes through a family.

WHO IS RESPONSIBLE FOR YOUR GOOD LOOKS?

o  Mom? Dad? Grandma? o  Unfortunately it is almost impossible to

associate a human trait with a single gene, really for 2 reasons: o  Things you think of as a single trait like eye or ear

shape are really polygenic, meaning they are controlled by many genes.

o  Second, many of your personal traits are only partly controlled by genetics

GENES AND THE ENVIRONMENT

�� Remember: phenotype is only partly controlled by genotype

�� Many genetic factors are strongly influenced by �� Environment

�� Nutrition �� Exercise

�� Ex. Bonsai Tree

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GENETICS AND THE ENVIRONMENT

o  The characteristics of any organism are not solely determined by genes inherited.

o  Characteristics are inherited by an interaction between genes and the environment. o  Tree has gene to grow

tall o  no rain and bad soil o  tree is stunted and small

b/c of environment

EXAMPLE: HEIGHT

�� Height is largely controlled by genetic factors

�� Improvements in nutrition has resulted in a 10cm increase in average height since the 1800s

…DIFFICULT TO STUDY HUMAN GENETICS

�� Humans have long generation times, complex life cycles, and relatively few offspring

MUTATIONS

MUTATIONS

�� Now and then cells make mistakes in copying their own DNA, inserting an incorrect base or even skipping a base as the new strand is put together.

�� These mistakes are called mutations, from a Latin word meaning “to change.”

�� Mutations are changes in the genetic material.

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KINDS OF MUTATIONS

�� 2 Kinds of mutations �� 1. Gene mutations: mutations that produce

changes in a single gene. �� Point Mutations

�� Often called base _________________________. �� Frameshift mutations

�� Caused by a base __________________ or _________________.

�� 2. Chromosomal mutations: those that produce changes in whole chromosomes

GENE MUTATIONS

Point mutations : gene mutations involve changes in one or a few nucleotides They occur at a single point in the DNA

sequence. Include:

Substitutions Insertions and deletions

SUBSTITUTIONS

�� Substitutions: one base is changed to another

�� Substitutions usually affect no more than a single amino acid.

INSERTIONS AND DELETIONS

�� Insertions and deletions: a base is inserted or removed from the DNA sequence

�� The effects of insertions or deletions can be much more dramatic.

�� Remember that the genetic code is read in three-base codons.

�� If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted for every codon that follows

GENE MUTATIONS

�� Frameshift mutations: shift the “reading frame” of the genetic message. �� Shift can change every

amino acid that follows the point of the mutation.

�� can alter a protein so much that it is unable to perform its normal functions.

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CHROMOSOMAL MUTATIONS

CHROMOSOMAL MUTATIONS

�� Chromosomal mutations cause changes in whole chromosomes

�� the number of chromosomes �� the structure of chromosomes

TYPES OF CHROMOSOMAL MUTATIONS

��  4 types of chromosomal mutations: ��  Deletions

��  involve the loss of all or part of a chromosome ��  Duplications

�� produce extra copies of parts of a chromosome ��  Inversions

��  reverse the direction of parts of chromosomes ��  Translocations

��  occur when part of one chromosome breaks off and attaches to another.

DELETIONS

�� Loss of all or part of a chromosome �� ABC-DEF 𐀌𐀧𐀻𐀾𐁎𐁏𐁞𐁟𐁠𐁡𐁢𐁣𐁤𐁥𐁦𐁧𐁨𐁩𐁪𐁫𐁬𐁭𐁮𐁯𐁰𐁱𐁲𐁳𐁴𐁵𐁶𐁷𐁸𐁹𐁺𐁻𐁼𐁽𐁾𐁿𐃻𐃼𐃽𐃾𐃿𐄃𐄄𐄅𐄆𐄴𐄵𐄶𐆋𐆌𐆍𐆎𐆏𐆜𐆝𐆞𐆟𐆠𐆡𐆢𐆣𐆤𐆥𐆦𐆧𐆨𐆩𐆪𐆫𐆬𐆭𐆮𐆯𐆰𐆱𐆲𐆳𐆴𐆵𐆶𐆷𐆸𐆹𐆺𐆻𐆼𐆽𐆾𐆿𐇀𐇁𐇂𐇃𐇄𐇅𐇆𐇇𐇈𐇉𐇊𐇋𐇌𐇍𐇎𐇏𐇾𐇿𐈀𐈁𐈂𐈃𐈄𐈅𐈆𐈇𐈈𐈉𐈊𐈋𐈌𐈍𐈎𐈏𐈐 AC-DEF

DUPLICATION

�� A segment of a chromosome is repeated �� ABC-DEF 𐀌𐀧𐀻𐀾𐁎𐁏𐁞𐁟𐁠𐁡𐁢𐁣𐁤𐁥𐁦𐁧𐁨𐁩𐁪𐁫𐁬𐁭𐁮𐁯𐁰𐁱𐁲𐁳𐁴𐁵𐁶𐁷𐁸𐁹𐁺𐁻𐁼𐁽𐁾𐁿𐃻𐃼𐃽𐃾𐃿𐄃𐄄𐄅𐄆𐄴𐄵𐄶𐆋𐆌𐆍𐆎𐆏𐆜𐆝𐆞𐆟𐆠𐆡𐆢𐆣𐆤𐆥𐆦𐆧𐆨𐆩𐆪𐆫𐆬𐆭𐆮𐆯𐆰𐆱𐆲𐆳𐆴𐆵𐆶𐆷𐆸𐆹𐆺𐆻𐆼𐆽𐆾𐆿𐇀𐇁𐇂𐇃𐇄𐇅𐇆𐇇𐇈𐇉𐇊𐇋𐇌𐇍𐇎𐇏𐇾𐇿𐈀𐈁𐈂𐈃𐈄𐈅𐈆𐈇𐈈𐈉𐈊𐈋𐈌𐈍𐈎𐈏𐈐 ABBC-DEF

INVERSION

�� Part of a chromosome becomes oriented in the reverse of its usual direction. �� ABC-DEF 𐀌𐀧𐀻𐀾𐁎𐁏𐁞𐁟𐁠𐁡𐁢𐁣𐁤𐁥𐁦𐁧𐁨𐁩𐁪𐁫𐁬𐁭𐁮𐁯𐁰𐁱𐁲𐁳𐁴𐁵𐁶𐁷𐁸𐁹𐁺𐁻𐁼𐁽𐁾𐁿𐃻𐃼𐃽𐃾𐃿𐄃𐄄𐄅𐄆𐄴𐄵𐄶𐆋𐆌𐆍𐆎𐆏𐆜𐆝𐆞𐆟𐆠𐆡𐆢𐆣𐆤𐆥𐆦𐆧𐆨𐆩𐆪𐆫𐆬𐆭𐆮𐆯𐆰𐆱𐆲𐆳𐆴𐆵𐆶𐆷𐆸𐆹𐆺𐆻𐆼𐆽𐆾𐆿𐇀𐇁𐇂𐇃𐇄𐇅𐇆𐇇𐇈𐇉𐇊𐇋𐇌𐇍𐇎𐇏𐇾𐇿𐈀𐈁𐈂𐈃𐈄𐈅𐈆𐈇𐈈𐈉𐈊𐈋𐈌𐈍𐈎𐈏𐈐 AED-CBF

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TRANSLOCATION

�� Part of one chromosome breaks off and attaches to another chromosome. �� ABC-DEF 𐀌𐀧𐀻𐀾𐁎𐁏𐁞𐁟𐁠𐁡𐁢𐁣𐁤𐁥𐁦𐁧𐁨𐁩𐁪𐁫𐁬𐁭𐁮𐁯𐁰𐁱𐁲𐁳𐁴𐁵𐁶𐁷𐁸𐁹𐁺𐁻𐁼𐁽𐁾𐁿𐃻𐃼𐃽𐃾𐃿𐄃𐄄𐄅𐄆𐄴𐄵𐄶𐆋𐆌𐆍𐆎𐆏𐆜𐆝𐆞𐆟𐆠𐆡𐆢𐆣𐆤𐆥𐆦𐆧𐆨𐆩𐆪𐆫𐆬𐆭𐆮𐆯𐆰𐆱𐆲𐆳𐆴𐆵𐆶𐆷𐆸𐆹𐆺𐆻𐆼𐆽𐆾𐆿𐇀𐇁𐇂𐇃𐇄𐇅𐇆𐇇𐇈𐇉𐇊𐇋𐇌𐇍𐇎𐇏𐇾𐇿𐈀𐈁𐈂𐈃𐈄𐈅𐈆𐈇𐈈𐈉𐈊𐈋𐈌𐈍𐈎𐈏𐈐 ABC-JKL GH-IJKL GH-IDEF

NONDISJUNTION ��  The most common error during meiosis ��  Occurs when the chromosomes fail to separate

��  It means “not coming apart” ��  If nondisjunction occurs, abnormal numbers of chromosomes

find their way into gametes, and a disorder of chromosome numbers may result. ��  Down’s , Turner’s, and Kleinfelter’s

WHAT CAUSES NONDISJUNCTION TO OCCUR?

��  As women age they are more likely to have offspring with trisomy 21

��  Meiosis begins in a girl’s ovaries before she is born but pauses until puberty, where only one egg completes meiosis each month until menopause.

��  This means that a cell might remain stopped in the middle of meiosis for decades. ��  It seems that the longer the time

lag, the greater the chance that there will be errors such as nondisjunction when meiosis is finally completed.

��  Some researchers hypothesize that damage to the cell during this lag time contributes to errors in meiosis.

NONDISJUNCTION

o  Polyploidy is a condition in which an organism has extra sets of chromosomes due to nondisjunction.

FINDING HUMAN DISORDERS

�� Many human disorders have become known through the study of genetic disorders.

�� In most cases the presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype.

CATEGORIES OF GENETIC DISORDERS

! Chromosomal !  Extra chromosome !  Missing part of chromosome

! Autosomal !  Recessive !  Dominant (less common)

! Sex-Linked !  Found on sex chromosome !  Differently expressed between males and females

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GENETIC DISORDERS PROJECT

! Work in pairs ! Disorders randomly assigned ! ONE page fact sheet using Google Docs ! Template for project with be shown ! Use ONLY high quality websites

beyond mendelian genetics in cases in which 2 or more … · 2020-02-04 · 2/4/20 1 beyond...

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