1. 7.1 Chromosomes and Phenotype
KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

5. Two copies of each autosomal gene affect phenotype.
7.1 Chromosomes and Phenotype
Two copies of each autosomal gene affect phenotype.
Mendel studied autosomal gene traits, like hair texture.

6. 7.1 Chromosomes and Phenotype
Mendel’s rules of inheritance apply to autosomal genetic disorders.
A heterozygote for a recessive disorder is a carrier.
Disorders caused by dominant alleles are uncommon.
(dominant)

7. Males and females can differ in sex-linked traits.
7.1 Chromosomes and Phenotype
Males and females can differ in sex-linked traits.
Genes on sex chromosomes are called sex-linked genes.
Y chromosome genes in mammals are responsible for male characteristics.
X chromosome genes in mammals affect many traits.

8. 7.1 Chromosomes and Phenotype
Male mammals have an XY genotype.
All of a male’s sex-linked genes are expressed.
Males have no second copies of sex-linked genes.

9. 7.1 Chromosomes and Phenotype
Female mammals have an XX genotype.
Expression of sex-linked genes is similar to autosomal genes in females.
X chromosome inactivation randomly “turns off” one X chromosome.

10. 7.2 Complex Patterns of Inheritance
KEY CONCEPT Phenotype is affected by many different factors.

11. Phenotype can depend on interactions of alleles.
7.2 Complex Patterns of Inheritance
Phenotype can depend on interactions of alleles.
In incomplete dominance, neither allele is completely dominant nor completely recessive.
Heterozygous phenotype is intermediate between the two homozygous phenotypes
Homozygous parental phenotypes not seen in F1 offspring

12. 7.2 Complex Patterns of Inheritance
Codominant alleles will both be completely expressed.
Codominant alleles are neither dominant nor recessive.
The ABO blood types result from codominant alleles.
Many genes have more than two alleles.

13. Many genes may interact to produce one trait.
7.2 Complex Patterns of Inheritance
Many genes may interact to produce one trait.
Polygenic traits are produced by two or more genes.
Order of dominance: brown > green > blue.

14. 7.2 Complex Patterns of Inheritance
An epistatic gene can interfere with other genes.

15. The environment interacts with genotype.
7.2 Complex Patterns of Inheritance
The environment interacts with genotype.
Phenotype is a combination of genotype and environment.
The sex of sea turtles depends on both genes and the environment
Height is an example of a phenotype strongly affected by the environment.

16. 7.3 Gene Linkage and Mapping
KEY CONCEPT Genes can be mapped to specific locations on chromosomes.

17. 7.3 Gene Linkage and Mapping
Genetics Experiments
Mendel – crossed pea plants
Conclusions: two alleles for each trait; alleles assort independently
Punnett and Bateson – crossed peas, found ratios different from 9:3:3:1
Conclusions: some traits must be linked

18. Gene linkage was explained through fruit flies.
7.3 Gene Linkage and Mapping
Gene linkage was explained through fruit flies.
Morgan – used fruit flies and found that linked traits are on the same chromosome.
Chromosomes, not genes, assort independently during meiosis.
Wild type
Mutant

19. 7.3 Gene Linkage and Mapping
Linked genes are not inherited together every time.
Chromosomes exchange homologous genes during meiosis.

20. 7.3 Gene Linkage and Mapping
Sturtevant
Sturtevant’s hypothesis: frequency of crossovers during meiosis related to distance between genes – more distance has cross-overs more often
Experiments: looked at fruit flies – recorded percentage crossing over happened between two genes, then used the percentages to make linkage maps

21. Linkage maps estimate distances between genes.
7.3 Gene Linkage and Mapping
Linkage maps estimate distances between genes.
The closer together two genes are, the more likely they will be inherited together.
Cross-over frequencies are related to distances between genes.
Linkage maps show the relative locations of genes.

22. 7.3 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

23. 7.4 Human Genetics and Pedigrees
KEY CONCEPT A combination of methods is used to study human genetics.

24. Human genetics follows the patterns seen in other organisms.
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.

25. Females can carry sex-linked genetic disorders.
7.4 Human Genetics and Pedigrees
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 Y

26. 7.4 Human Genetics and Pedigrees
Sex-linked Disorders
Sex-linked in males: see disorder much more often in males – no 2nd X chromosome, can’t be carriers
Sex-linked in females: only have disorder if they have 2 recessive alleles – can be carriers

27. 7.4 Human Genetics and Pedigrees
Tracing Autosomal Genes
Tracing Sex-linked Genes
Equal numbers of males and females have it
More males than females will have it; females can be carriers
People with recessive phenotype must be homozygous recessive
Females with recessive phenotype have two recessive alleles; males only have one
People with dominant phenotype can be homozygous dominant or heterozygous
Heterozygous phenotypes don’t show the recessive phenotype – are carriers
Two heterozygotes can have offspring of either phenotype
Female carriers can pass on recessive allele to either male or female offspring
Or genotype
Males with recessive can pass on recessive allele only to females

28. A pedigree is a chart for tracing genes in a family.
7.4 Human Genetics and Pedigrees
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.

29. 7.4 Human Genetics and Pedigrees
If the phenotype is more common in males, the gene is likely sex-linked.

30. Several methods help map human chromosomes.
7.4 Human Genetics and Pedigrees
Several methods help map human chromosomes.
A karyotype is a picture of all chromosomes in a cell.
X Y

31. 7.4 Human Genetics and Pedigrees
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