1. Human Genetics Chapter 7

2. The Role of Chromosomes
A. 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 chromosomes
Fly – 8 chromosomes
Cat – 38 chromosomes 23
23 PAIRS

3. 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 X
chromosomes (XX)
- Autosomes do not determine a
person’s gender. They are body
chromosomes. They determine
ones characteristics!
- Chromosome #1-22

4. X & Y Chromosomes & Traits
X chromosome much larger than the Y

5. A way to tell chromosome number
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.
Karyotype

6. Human Traits
A. 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= Red
WW= White
If a red snap dragon were crossed with white snapdragon, the heterozygous plant would be PINK!
RR x WW
Offspring = RW = pink

7. - Both phenotypes are shown in the Heterozygous individual.
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. B B W BW BW W BW BW

8. More Codominance Normal Red Blood Cell Sickled Red Blood Cell
African American Population
Resistance to Malaria

9. 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.
Parent genotypes:
Genotypes:
Phenotypes:

10. Co-dominance and Multiple Alleles in Blood Types
Example: Blood Types
The four blood types are Type A, Type B, Type AB, Type O

11. Codominant alleles will both be completely expressed.
Codominant alleles are neither dominant nor recessive.
The ABO blood types result from codominant alleles.
The 3 multiple alleles are A, B, and O
A and B are always dominant to O (i).
IAi = _____ type blood IAIA = _____ type blood
IBIB = _____ type blood IBi = ____ type blood

12. A and B are NOT dominant to each other, they are Codominant
AB genotype would look like this… IAIB
So remember… There are 3 alleles (A, B, O), however there are 4 blood types. (A, B, AB, O)

13. IA i IA IAIA IBi IAi IAIB IB Genes Blood type ii O type IAIB AB type
IAIA or IAi A type
IBIB or IBi B type
Cross a woman Heterozygous for A-blood and a man with AB-blood
Parent genotypes:
Genotypes:
Phenotypes: IA
IAIA
IBi
IAi
IAIB IB
IAi x IAIB
1IAIA:1IAIB:1IAi:1IBi
1: AB type
2: A-type
1: B-type

14. 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
1:BB
2:Bb
1:bb
1:BB
2:BW
1:WW
1:BB
2:BW
1:WW
1:Black
2:Black & White
1:White
3:Black
1:White
1:Black
2:Grey
1:White

15. Polygenic Traits Polygenic traits are produced by two or more genes.
This occurs when many genes interact to produce one trait.
Order of dominance: brown > green > blue.
Example: Eye Color, skin color, height

16. 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
Female that has the disorder
Female carrier for a disorder X
Male that has the disorder

17. 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

18. 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. X Y X

19. Colorblindness - is a sex-linked recessive trait
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
______________________________________ 2 1
The male only needs one gene

20. What do you see?

21. A woman is heterozygous for Normal vision
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
X N Xn Y
Parent genotypes: XN Xn x XnY
Mom Dad
FIND THE:
Genotypic Ratio: Phenotypic Ratio:

22. Genotypic Ratio 1XNXn : 1XnXn : 1 XNY : 1 XnY
Answer:
LET … N = normal vision and n = color blind
MOM = heterozygous normal vision. XN Xn
DAD = colorblind. XnY
Genotypic Ratio 1XNXn : 1XnXn : 1 XNY : 1 XnY
Phenotypic Ratio 1 normal female carrier : 1 colorblind female : 1 Normal male : 1 colorblind male
X N Xn Y
XN Xn
Xn Xn
XN Y
Xn Y

23. 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.

24. 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

25. 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.