1. 7.1 Chromosomes and Phenotype
Two copies of each autosomal gene affect phenotype (physical).
Mendel studied autosomal gene traits, like hair texture.
Autosome – chromosome with genes not related to sex of organism (body cells)
Compared to:
Sex Chromosomes: control the development of sexual characteristics

2. 7.1 Chromosomes and Phenotype
Carrier – has an allele for a trait or disease that is not expressed.
Carrier does not have disease symptoms but can pass it on to offspring.
Does not have disorder
(dominant)
Dominant allele disorders are rare.
Huntington’s disease is an example of a disease caused by a dominant allele.
Has disorder

3. 7.1 Chromosomes and Phenotype
Genes on sex chromosomes are called sex-linked genes.
Y chromosome - male characteristics .
X chromosome - genes affects many traits. .
Males can pass on X or Y
Females only pass on X

4. 7.1 Chromosomes and Phenotype
Who determines the sex of the offspring? FATHER
Father – he can provide an X or Y chromosome
Egg X X X XX XX XY XX X X
Body Cell X XY Y Y
Sperm
Body Cell
1female:1male

5. 7.1 Chromosomes and Phenotype
How are sex-linked genes expressed differently in phenotypes of males & females?
Males have an XY genotype; therefore...
All of a male’s sex-linked genes are expressed.
Males have no second copies of sex-linked genes to mask the effects of another allele. Therefore, you will see sex linked genetic disorders more often in males than females.
Y chromosome is much smaller

6. 7.1 Chromosomes and Phenotype
Females have an XX genotype.
X chromosome inactivation -randomly “turns off” one X chromosome.
Why are males more likely than females to have sex-linked genetic disorders?
All sex-linked genes are expressed in males, even recessive. Females have a backup X chromosome which can mask genetic disorders.

7. 7.1 Chromosomes and Phenotype
Page 203
Can you explain what is going on in this picture?
Why is there a color variation between the female & male calico cats?
The female calico cats have two chromosomes with different alleles for fur color. Both alleles are expressed in a random pattern. The male cat has only one X chromosome, and it’s allele for fur color is expressed across the entire body Xº = Orange fur Xº = Black fur allele

8. Complex Patterns of Inheritance
Color blindness is a problem in which red or green look like shades of gray or other colors.
The gene is carried on the X chromosome and is a recessive trait. XC Xc
XCXC
XCXc
XCY
XcY XC
XCXC = normal female
XCXc = female, normal vision (carrier)
XCY = normal vision male
XcY = color blind male Y
Neither female are colorblind – 1 female is a carrier however
1 male born normal & 1 male born colorblind

9. 7.2 Complex Patterns of Inheritance
Some traits are neither totally dominant nor totally recessive.
Incomplete dominance - when neither gene/allele is completely dominant nor completely recessive to the other
- Heterozygous phenotype is intermediate between the two homozygous phenotypes
Example: White flowers and red flowers produce pink flowers

10. Codominance RR RR’ R’R’ R = Round blood cells R’ = Sickle Cells
When both alleles of a gene are expressed- neither is dominant or recessive
Sickle Cell Anemia
R = Round blood cells
R’ = Sickle Cells
Disease in which the body makes sickle-shaped red blood cells. Sickle-shaped cells don’t move easily through your blood vessels. They’re stiff and sticky and tend to form clumps and get stuck in the blood vessels . R R’ RR
RR’
R’R’ R
RR = normal blood
RR’ = some sickle cells, some normal cells
R’R’ = has sickle cell anemia R’

11. Complex Patterns of Inheritance
Codominant - alleles will both be completely expressed.
Example – red and white flower produce a flower with BOTH colors
Codominant alleles are neither dominant nor recessive.
The ABO blood types result from codominant alleles.
Many genes have more than two alleles.

12. Complex Patterns of Inheritance
Polygenic traits are produced by two or more genes.
Order of dominance: brown > green > blue.

13. 7.2 Complex Patterns of Inheritance
Epistatic gene - can interfere with the expression of all other genes.
Mice have 5 genes that control fur color.
2 genes for general color
1 for shading
1 for spots
1 epistatic gene for color that overrules all other genes

14. 7.2 Complex Patterns of Inheritance
Phenotype is a combination of genotype and environment.
The sex of sea turtles depends on both genes and the environment. Warm eggs develop into females
Height is an example of a phenotype strongly affected by the environmental factors such as early nutrition and health care.

15. 7.3 Gene Linkage and Mapping
Gene linkage was explained through fruit flies.
(b/c could quickly and cheaply grow new generations)
Morgan found that linked traits are on the same chromosome. Traits can be inherited as a group.
Chromosomes, not genes, assort independently during meiosis.
Wild type
Mutant
Common
phenotype
Different
phenotype

16. Famous Scientist Punnett & Bateson said: (invented the punnett square)
Suggested some genes are linked together
Morgan said:
Chromosomes, not genes assort independently.
Mendel said:
Genes assort independently of one another.
Sturtevant (Morgan’s student) said: frequency of cross- overs was related to the distance bw genes.

17. Gene Linkage and Mapping
Linked genes are not inherited together every time.
Gene linkage: the tendency: for genes located close together on a chromosome to be inherited together.
Chromosomes exchange homologous genes during meiosis.
Genes
Close
together

18. 7.3 Gene Linkage and Mapping
Linkage maps – map of location of genes on a chromosome.
The closer together two genes are, the more likely they will be inherited together.
Cross-over frequencies are related to distances between genes. How frequently a cross over will occur is related to the distance bw the genes!

19. Gene Linkage and Mapping
Cross-over frequencies can be converted into map units.
gene A and gene B cross over 6.0 percent of the time
gene B and gene C cross over 12.5 percent of the time
gene A and gene C cross over 18.5 percent of the time

20. Study Guide worksheet page 44 Linkage Map 7.3
Cross-Over Frequencies:
A-B 20%
B-C 5%
A-C 25%
A-D 7%
D-B 13% 20-7=13
D-C 18% 25-7=18 A D B C 7 20 25

21. 7.4 Human Genetics and Pedigrees
Human genetics follows the patterns seen in other organisms.
The basic principles of genetics are the same in all sexually reproducing organisms.
Inheritance of many human traits is complex.
Single-gene traits are important in understanding human genetics.

22. Gene Linkage and Mapping
Females can carry sex-linked genetic disorders.
Males (XY) express all of their sex linked genes.
Expression of the disorder depends on which parent carries the allele and the sex of the child.
X chromosome carries about 1100 genes while the Y carries about 250

23. Gene Linkage and Mapping
Pedigree - chart used 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.
How can you tell if a chromosome is a autosome or a sex chromosome?
If the same # of male & female have the phenotype then the gene is most likely autosome.
Widow’s peak: W = widow’s peak w = non widow’s peak

24. Gene Linkage and Mapping
If the phenotype is more common in males, the gene is likely sex-linked.
Colorblindness: M = normal vision m = colorblindness

25. Gene Linkage and Mapping
Several methods help map human chromosomes.
Karyotype - a picture of all chromosomes in a cell. Shows changes in chromosomes. Ex: if you have an extra chromosome
X Y
Two methods used to study human chromosomes:
1.Pedigrees
2. Karyotypes

26. Gene Linkage and Mapping
Karyotypes can show changes in chromosomes.
deletion of part of a chromosome or loss of a chromosome
large changes in chromosomes
extra chromosomes or duplication of part of a chromosome