human genetics chapter 7 1. the role of chromosomes a. chromosome number 1.each human sperm/egg has...
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Human Genetics
Chapter 7
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The Role of ChromosomesA. Chromosome number
1. Each human sperm/egg has 23 chromosomes
2. Each human body cell has 23 pairs of chromosomes
3. Each type of organism has a different number of chromosomes.
Humans - 46 chromosomes
Fly – 8 chromosomes
Cat – 38 chromosomes
23 23
23 PAIRS
The Role of Chromosomes
Chromosome number- The last pair of chromosomes,or the 23rd pair are called the sex chromosomes.- Males have an X and a Y chromosome (XY)- Females have two Xchromosomes (XX)
- Autosomes do not determine aperson’s gender. They are body chromosomes. They determine ones characteristics!
- Chromosome #1-22 3
• X & Y Chromosomes& Traits
• X chromosome much larger than the Y
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Amniocentesis, a sampling of the fetal fluid which then can help determine if there are any genetic disorders of the developing fetus.
Geneticist will look at the chromosomes of the fetus.
A way to tell chromosome number
Karyotype
Human TraitsA. Incomplete dominance, neither allele/gene is completely
dominant nor completely recessive.
- Heterozygous phenotype is in between the two homozygous phenotypes
- individual is a blend
Snap dragons (flowers)RR= Redww= White
If a red snap dragon were crossed with white snapdragon, the heterozygous plant would be PINK!
RR x ww
Offspring = Rw = pink6
B. Codominance- Codominant alleles/genes are both fully and separately expressed.
- Both phenotypes are shown in the Heterozygous individual.
- Black hamster crossed with a white hamster- BB X WW
- The heterozygous
individual BW, would
be both black and white
in color.7
B B
W
W
BW
BW
BW
BW
Co-dominance and Multiple Alleles in Blood Types
Example: Blood Types
The four blood types are Type A, Type B, Type AB, Type O
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The 3 multiple alleles are A, B, and O
• A and B are always dominant to O.– AO = A type blood– BO = B type blood
• A and B are NOT dominant to each other, they are Codominant
So remember… There are 3 alleles (A, B, O), however there are 4 blood types. (A, B, AB, O)
Genes Blood type
OO O type
AB AB type
AA or AO A type
BB or BO B type
Cross a woman Heterozygous for A-blood and a man with AB-blood
–Parent genotypes:
–Genotypes:
–Phenotypes:
A
OA
B
AA
BO
AO
AB
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AO x AB
1AA:1AB:1AO:1BO
1: AB type2: A-type1: B-type
More Codominance
Sickled RedBlood Cell•African American
Population•Resistance to Malaria
Normal RedBlood Cell
Sickle Cell • NN= Normal Blood Cells
• SS= Sickled Blood Cells
• NS = Both Normal and Sickled Cells
• Cross a heterozygous mom with a heterozygous dad for blood cells.
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Parent genotypes: Genotypes: Phenotypes:
NOW YOU TRY: Bb x Bb as Complete, Incomplete, & Co- Dominance
Say that:B = Black
b = White
W = White
Complete Dominance
Incomplete Dominance
Co-Dominance
Genotype Ratio
Phenotype Ratio
1BB:
2Bb:
1bb
1BB:
2Bb:
1bb
1BB:
2BW:
1WW
3 Black :
1 White
1 Black :
2 Gray :
1 White
1 Black:
2 Black & White:
1 White
Polygenic Traits• Polygenic traits are produced by two or more
genes.
• This occurs when many genes interact to produce one trait.
• Example: Eye Color, skin color, height
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C. Sex-linked traits - Genes on the X chromosome
1. Only the X Chromosome carries genes
so if a gene is on the X chromosome, the female would have TWO of those genes
and the male would have only ONE.
X Y
X X
Female that has the disorder Female carrier for a disorder
Male that has the disorder
C.Sex-linked traits- A genetic disorder that is found or linked to the X
chromosome ONLY- Females can carry a sex-linked genetic disorder and
not have the disorder.- This is known as being a carrier of the disorder.- In order for the female to have the disorder both X
chromosomes must have the gene for the disorder
- Males (XY) express all of their sex linked genes because they only have one X chromosome.
- If the X chromosome has the gene, the male has the disorder.
- Males can not be carriers because they only have one X chromosome
- Examples: Hemophilia and Colorblindness 17
X Y X X
1. Colorblindness
a sex-linked recessive trait. (C- normal vision; c- colorblindness)
• In order for a female to be color blind, she would have to have two colorblind genes.
• A male needs to only have one colorblind gene.
Colorblindness - is a sex-linked recessive trait. (C- normal vision; c- colorblindness)
• In order for a female to be color blind, she would have to have this many colorblind genes. _______
• A male needs to have this many _______
• It is more likely to have a colorblind male than a colorblind female because
______________________________________
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2
1
The male only needs one gene
What do you see?
A woman is heterozygous for Normal vision. She marries a man who is colorblind.
What is the predicted colorblindness outcome for their children?
LET … N = normal vision and
n = color blind
Parent genotypes:
XN Xn x XnY
Mom Dad
FIND THE:Genotypic Ratio: Phenotypic Ratio:
X N Xn
Xn
Y
Answer:
LET … N = normal vision and n = color blind
MOM = heterozygous normal vision. XN Xn
DAD = colorblind. XnY
X N Xn
Xn
Y XN Y
Xn XnXN Xn
Xn Y
Genotypic Ratio
1XNXn : 1XnXn : 1 XNY : 1 XnY
Phenotypic Ratio
1 normal female carrier : 1 colorblind female :
1 Normal male : 1 colorblind male 22
X Chromosome Inactivation• Males and females can differ in sex linked traits.
– The expression of genes on the sex chromosomes differs from the expression of autosomal genes.
– Genes located on the sex chromosomes are called sex- linked genes or X-linked genes.
– Males express all of the alleles on both sex chromosomes.– In females one of the two X chromosomes is randomly
turned off by a process called X chromosome inactivation.
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Environment + Genes• Your phenotype is not just dependent on your
genes, but also the environment
• Examples– Sea turtles gender –determined by the temp of
sand– Gender of alligators – determined by temp.– Height of people- influenced by nutrition
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A pedigree is a chart for tracing genes in a family.
• Phenotypes are used to infer genotypes on a pedigree.• Autosomal genes show different patterns on a pedigree than
sex-linked genes.
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