inheritance of chromosomes (dna) inheritance of genes packets/18 genetics/18 gen… · ·...

Inheritance of chromosomes (DNA)

� egg + sperm →→→→ zygote

egg

sperm

zygote

Inheritance of genes

� on the chromosomes passed from Mom & Dad to offspring are genes for a trait

�may be same information

�may be different information

eye color

(blue or

brown?)

eye color

(blue or

brown?)

Effect of genes

� _____________________________________

� ex. brown vs. blue eyes

� ex. brown vs. blonde hair

� different forms of genes are called _______

What will we find out?

� genes come in “versions”

� brown (B) vs. blue (b) eye color

� __________________________________

� alleles are inherited separately from each parenteach parent

� brown (B) & blue (b) eye colors are

separate & do not blend

� either have brown or blue eyes, not brue

� Some alleles mask others

� brown (B) eye color masks blue (b)

� that’s why we capitalized brown!

Genes affect what you look like…

X

BBbb

Bb Bb Bb Bb

X

Bbbb

Bb Bb bb bb

X

BbBb

BB or Bb BB or Bb BB or Bb bb

How does this work?

eye

color

(brown?)

eye

color

(blue?)

� paired chromosomes have same kind of genes

� but may be different alleles

hair

color

hair

color

(brown?)(blue?)

Making gametes

BB = brown eyes

bb = blues eyes

Bb = brown eyes

BB

B

B

b

bb

Bb

→→→→ brown is ________ over blue

→→→→ blue is ________ to brown

b

B

b

BB = brown eyes

bb = blues eyes

2 of the same alleles

____________ BB

B

B

bhomozygous dominant (brown)

Bb = brown eyes

2 different alleles

____________

bb

b

Bb

B

b

homozygous dominant (brown)

homozygous recessive (blue)

Genetics vs. appearance

� There can be a difference between how an organism looks & its

genetics

�_________________ = phenotype�_________________ = phenotype

� brown eyes vs. blue eyes

�_________________ = genotype

�BB, Bb, bb

2 people can have the same appearance but

have different genetics: BB vs Bb

� Modern genetics began in the mid-1800s in an abbey garden, where a

monk named Gregor Mendel

genetics: __________________

___________________________

___________________________

___________________________

monk named Gregor Mendel

documented inheritance in peas

� used good experimental design

� used mathematical analysis

� collected data & counted them

� excellent example of scientific

method

Mendel chose peas wisely

� Pea plants are good for genetic research

� ______________________ with distinct

heritable features with different variations

� flower color, seed color, seed shape, etc.

____________________________________� ____________________________________

____________________________________

� each pea plant has male & female structures

� pea plants can self-fertilize

� Mendel could also cross-pollinate plants:

moving pollen from one plant to another

Mendel chose peas luckily

� Pea plants are good for genetic research

� ____________________________________

� most characters are controlled by

a single gene

� each gene has only 2 alleles, � each gene has only 2 alleles,

(forms of a gene) one of which

is completely “dominant” over

the other

Pollen transferred from white flower to stigma of purple flower

� he bred easy-to-grow pea plants

� cross-pollinate

true breeding

parents

� raised seed and

white X white

white X white

white X white

purple X purple

purple X purple

purple X purple

all purple flowers result

?

self-pollinate

� raised seed and

then observed

easy-to-see traits

� allowed offspring

to self-pollinate

& observed next

generation

Looking closer at Mendel’s work…

Parentsgeneration

(P)

1st

Xtrue-breeding

purple-flower peastrue-breeding

white-flower peas

2ndgeneration

(F2)

1stgeneration(F1 hybrids)

self-pollinate

What did Mendel’s findings mean?

I. Mendel’s Principal of Dominance

� purple & white flower colors are separate traits that do not blend � purple x white ≠ light purple

I’ll speak for both of us!

� purple x white ≠ light purple

� purple masked white

� dominant allele� masks other alleles

� __________________________________________________________

� recessive allele� not expressed when dominant allele is present

homologous

chromosomes


� traits come in alternative versions that can be passed down

� purple vs. white flower color

� alleles = different forms of a gene� different alleles vary in the sequence of � different alleles vary in the sequence of nucleotides (DNA letters) in the code

purple-flower allele &

white-flower allele are

2 DNA variations at

flower-color spot

different versions of

gene on homologous

chromosomes

Dominant ≠ most common allele

� Because an allele is dominant does not mean…

� it is better, or

� it is more common

Polydactyly

dominant allele

Polydactyly

the allele for >5 fingers/toes

is DOMINANT & the allele for

5 digits is recessive

individuals are born with

extra fingers or toes

recessive allele far morecommon than dominant→→→→only 1 individual out of 500

has more than 5 fingers/toes

→→→→so 499 out of 500 people are homozygous recessive (aa)

� homologous (similar) chromosomes have the same order of genes…however…

� these chromosomes might not have the exact ________________ of a gene!

� these different forms are called ________


� these different forms are called ________

� ex. eye colors: brown, hazel, green, blue

eye

color

eye

color

� in simple patterns of inheritance, there are two different forms of a gene (alleles),

where one is __________ and one is

__________

� DOMINANT IS SHOWN WITH CAPITALS


� DOMINANT IS SHOWN WITH CAPITALS

� recessive is shown with lowercase

R – round seeds

r – wrinkled

Q – six fingers

q – five fingers

A – not-albino

a – albino

B – brown eyes

b – blue eyes

T – tall plants

t – short plants

P – purple

p – white

Y – yellow seeds

y – green seeds

Genotype vs. phenotype

� difference between how an organism “looks” & its genetics

� ____________

� “physical” description of an organism’s trait

____________� ____________

� description of an organism’s genetic

makeup

� shown by letters!

Explain Mendel’s results using

dominant & recessive

phenotype & genotype F1

P X

purple white

all purple

Making crosses

� can represent genotypes alleles as letters

� flower color alleles →→→→

� true-breeding purple-flower peas →→→→

� true-breeding white-flower peas →→→→

x

F1

P X

purple white

all purple

Describing Genotypes

� the 2 copies of the gene can be the same � homozygous = same alleles = PP, pp

� the 2 copies of the gene can be the different� heterozygous = different alleles = Pp


II. Mendel’s Principal of Segregation and Recombination

� when gametes are formed during meiosis (DIPLOID �� HAPLOID), the homologous chromosomes (which may contain the different allelic forms of a gene) separate randomlyallelic forms of a gene) separate randomly

� this is called ____________________



� if the organism has a ______________ (the same alleles) genotype for a given trait, then all gametes will also have that allele for that trait

PP

P

P

pp

p

p



� if the organism has a ________________ (NOT the same alleles) genotype for a given trait, then halfof the gametes will have one allele and the other half will have the other allele

Pp

P

p

half will have the other allele



� when the haploid gametes fuse during fertilization, the diploid number of chromosomes is restored

this can result in a new combination of alleles!� this can result in a new combination of alleles!

� this is called ____________________

Parentsgeneration

(P)

1st

Xtrue-breeding

purple-flower peastrue-breeding

white-flower peas

PP pp

Looking even closer at Mendel’s work…

2ndgeneration

(F2)


self-pollinate

Pp Pp Pp Pp

????

P p

male / sperm

PP

75%

25%

50%

% genotype % phenotype

Pp

1stgeneration(hybrids)

To show segregation and recombination, we use

Punnett squares!

Pp x Pp

P

p

female / eggs

25%

50%

25%

PP Pp

Pp pppp

Pp

Punnett squares

Bb x Bb

male / sperm

X

female / eggs

Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares

and you will not get the answer wrong!

Problem:

A homozygous tall pea plant is crossed with a short pea

plant. In pea plants, tall is dominant over short. What

would the expected phenotypes (phenotypic ratio) and

genotypes (genotypic ratio) of their offspring?genotypes (genotypic ratio) of their offspring?

STEP #1set up the key that

will show how each

haploid allele and

each diploid

combination will be

represented



Problem:





STEP #2set up the parents

that will be crossed;

use the information

from the word

problem itself!



Problem:





STEP #3carry out the Punnett

square; that is, put

one parent’s

segregated alleles on

top, and the other on

the left…then fill in



Problem:





STEP #4determine the ratios

of the cross;

phenotypes describe

their appearance,

genotypes describe

their alleles



Problem:




genotypes (genotypic ratio) of their offspring?

Tt Tt

Tt Tt

tall tall

tall tall

hetero-

zygous

hetero-

zygous

hetero-

zygous

hetero-

zygous

genotypes (genotypic ratio) of their offspring?

t

t

T Tphenotypic ratio

genotypic ratio

Problem #1:

Use a Punnett square to show the offspring of a

cross between two pea plants that are heterozygous

for height (Tt). Give the expected phenotypic and

genotypic ratios of the offspring

phenotypic ratio genotypic ratio

Problem #2:


cross between a pea plant that is homozygous tall

and one that is heterozygous. Give the expected

phenotypes and genotypes of the offspring.


Problem #3:

In pea plants, yellow seeds are dominant over green

seeds. What would the phenotypic and genotypic

ratios be from a cross between a homozygous green

seeded plant and a pea plant that is a hybrid for

seed color?


Test cross

PP?

If an organism has the dominant phenotype, how

can we tell if it is homozygous dominant (AA) or

heterozygous (Aa)

PP?

Pp?

x

PP pp

Test cross

p p p p

x

Pp pp

p p

P

P

Pp

Pp Pp

Pp

p p

P

p

Pp

pp pp

Pp

Intermediate Patterns of Inheritance

� Mendel worked with a simple system

� peas are genetically simple

�most traits are controlled by single gene

� each gene has only 2 version

� 1 completely dominant (A)� 1 completely dominant (A)

� 1 recessive (a)

� But its usually not that simple!

A) Incomplete dominance

� __________________________________________________________________________

� hybrids have “in-between/blended” appearance

�RR = red flowers

� rr = white flowers

→→→→

→→→→� rr = white flowers

�Rr = pink flowers� make 50% less color

RR Rr rr

→→→→

→→→→

100% pink flowers

X

1st

Parentgeneration

(P)true-breedingred flowers

true-breeding white flowers

RR R′R′

4 O’clock

flowersA) Incomplete dominance

2ndgeneration

(F2)


RR′RR′RR′RR′

self-pollinate

25%white

25%red

50%pink

R R′male / sperm

25%

%

genotype

%

phenotype

RR 25%

RR′ x RR′

A) Incomplete dominance

R R′

R

R′

female / eggs RR

RR′ R′R′

RR′

25%

1:2:1

50%

25%

1:2:1

RR′

RR′

R′R′

50%

Problem #4:


cross between a red Four O’clock flower and one

that is heterozygous. State the phenotypic and

genotypic ratio of the offspring of the cross.


Problem #5:

What would the phenotypic and genotypic ratios be

of the offspring produced from a cross bewteen a

white Four O’clock flower and one that is pink?


B) Codominance

� __________________________________________________________________________

�RR = red coat color

� rr = white coat color

�Rr = pink coat color?

→→→→

→→→→

→→→→

Problem #6:

What would the phenotypic and genotypic ratios be

from the cross between two roan cattle?


C) Multiple Alleles

� when there are more than just 2 alleles for a given trait

� human blood types are an example with ____________ ________________________________________________________________________

� alleles are A, B, i and code for ‘marker’ on red blood cells

� _________________________________, but…

� ______________________ each other (that means are equally expressed)

pheno-

typegenotype

antigen

on RBC

antibodies

in blood

donation

status

A AA orA itype A antigens

on surface anti-B antibodies __

A allele codes for the ________

B allele codes for the ________

i allele codes for ________

A AA orA i on surface

of RBC

anti-B antibodies __

B BB or B itype B antigens

on surface

of RBC

anti-A antibodies __

AB ABboth type A &

type B antigens

on surface

of RBC

no antibodiesuniversal recipient

O i ino antigens

on surface

of RBC

anti-A & anti-B

antibodies

universal

donor

Blood donation

clotting clotting

clotting clotting

clotting clotting clotting

Problem #7:

If a heterozygous A person and a homozygous B

person have children, can they have a baby with A

type blood?

Problem #8:

Four newborn babies in the delivery room were

accidentally mixed up by the nurse who attached the

wrong wristbands to each child. The blood types of the

four babies were known to be AB, O, A, and B. The blood

types of each set of parents are also known. Using your

knowledge of genetics, carry out all possible crosses to

determine which baby belongs to which set of parents.

(HINT: You may have to do two crosses for certain (HINT: You may have to do two crosses for certain

parents!)

Parental Set #1 : O and AB

Parental Set #2 : AB and B

Parental Set #3 : O and O

Parental Set #4 : O and A

A or B

AB or

A or B

O and AB

parents

AB and B

parentsor

only O

A or O

O and O

parents

O and A

parents or

D) Sex-Linked Traits

� most diploid organisms have two different types of chromosomes

1) autosomes: _________________________ ___________________________________• a.k.a. somatic chromosomes

2) sex chromosomes: ___________________ 2) sex chromosomes: ___________________ ____________________________________

� humans have 22 pair (44 total) of autosomes and 1 pair (2 total) of sex chromosomes

46 chromosomes

23 pairsdiploid (2n) = 2 copies

XX

diploid (2n) = 2 copies 46 chromosomes

23 pairs

XY


� __________________________________________________________________________

� _____________________________________ (50%-50% chance!)

� this occurs along with the segregation of all homologous autosomes during the homologous autosomes during the production of gametes—meiosis

� besides the genes for sex determination, other genes are found on these chromosomes too!

XX XY

Thomas Hunt Morgan

� embryologist at Columbia University

� 1st to associate a specific gene with a

specific chromosome

�Drosophila breeding

� 2 week generations� 2 week generations

� 4 pairs of chromosomes

� XX=female, XY=male

Thomas Hunt Morgan

� he noticed that some traits were inherited more frequently in males than

females

� ______________________________________________________________________________________________________

Thomas Hunt Morgan

� because the Y chromosome is actually smaller than the X chromosome, men

only have one copy of certain genes…

� so… if the X chromosome has a

recessive allele, that has to be recessive allele, that has to be

expressed because that is all that is

there!

YX


� for Punnett squares, there are different ways to

set up a key for a sex-linked recessive allele…

X = normal X

Y = normal Y

X = recessive X

XA= normal X

Y = normal Y

Xa= recessive X

XH Ymale / sperm

XHY

XH

HH HhxXHY XHXh


XH

Xh

female / eggs

XHXH

XHXh

XHY

XhYXHXh

XH

Xh

XHY

Y XHXH XHY

XHXh XhY

Problem #9:


cross between a woman with normal (not a carrier)

vision and a color-blind male. What percentage of

each sex would you expect this condition to occur?

Problem #10:


cross between a woman who carries the hemophilia

gene and a man who is a hemophiliac. What

percentage of each sex would you expect this

condition to occur?

inheritance of chromosomes (dna) inheritance of genes packets/18 genetics/18 gen… · ·...

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