1. Inheritance Patterns and Human Genetics
Chapter 12:
Inheritance Patterns and Human Genetics

2. Chromosomes and Inheritance
KEY CONCEPT Chromosomes are the mode of genetic inheritance in humans

3. Two Types of Human Chromosomes
Sex Chromosomes – contain genes that determine the gender (sex) of an individual

4. Two Types of Human Chromosomes
Autosomes – all other chromosomes which are not directly involved in gender determination

5. Gender (Sex) Determination
Read the first paragraph under the heading ‘Sex Determination’ on page 236.
SRY – Sex-determining Region Y: is a gene on the Y-chromosome that codes for a protein that causes the gonads of and embryo to develop as testes.

6. Sex-linked Trait – a trait coded by an allele on a sex chromosome
Sex-Linked Genes and Traits
Sex-linked Trait – a trait coded by an allele on a sex chromosome
Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex-linked trait.

7. The X-chromosome is much larger than the Y-chromosome
Sex-Linked Genes and Traits
The X-chromosome is much larger than the Y-chromosome
This causes there to be many more X-linked than Y-linked traits

8. Linked Genes
Linked Genes – pairs of genes that tend to be inherited together because they are close to each other on a chromosome
Because they are close to each other, they are less likely to be separated in crossing over during meiosis

9. Chromosome Mapping
Chromosome Map – a diagram that shows the linear order of genes on a chromosome
The percentage of crossing-over for two traits is proportional to the distance between them on a chromosome
Map Unit – a 1% frequency (chance) to cross over

10. They do not affect the organism itself but can be passed to offspring
Mutations
Germ-Cell Mutations – changes in nucleotide-base sequence that take place in an organism’s gametes
They do not affect the organism itself but can be passed to offspring

11. They can affect an organism but will not be passed on to offspring
Mutations
Somatic-Cell Mutations – changes in nucleotide-base sequence that take place in an organism’s body cells
They can affect an organism but will not be passed on to offspring

12. Chromosomal Mutations
Chromosome Mutation – changes in the structure of a chromosome or complete loss or gain of a chromosome

13. Types of Chromosomal Mutations
Deletion – loss of a piece of a chromosome
Inversion – chromosome segment breaks off, flips around, and reattaches

14. Types of Chromosomal Mutations
Translocation – a piece of chromosome breaks off and reattaches to a non-homolog
Nondisjunction – a chromosome fails to separate from its homologue during meiosis
Causes one gamete to receive an extra chromosome and one gamete to receive no copies

15. Human Genetics
KEY CONCEPT Geneticists analyze genetic data to track the factors that influence human genetic traits and their inheritance

16. Pedigrees
Pedigree – a diagram (tree) that shows how a trait is inherited over several generations
Squares are males
Circles are females
Filled symbols have the trait/condition
Empty symbols do not have trait or condition

17. Patterns of Inheritance – the expression of genes over generations
Pedigrees help interpret these patterns
Carrier – an organism that does not express the phenotype for a trait, but carries one recessive allele
A carrier can pass the allele to an offspring who might wind up showing the phenotype

18. Complex Characters
Complex Characters – traits influenced strongly by both the environment and by genes
Read the first two paragraphs on page 243
X-linked Traits – complex characters that are determined by genes found on the X-chromosome
Sex-Influenced Traits – autosomal traits where the same genotype in males and females will show as different genotypes

19. Genetic Disorders
We will go over Table 12-1 on page 246 and do a Punnett square for Tay-sachs to see how a carrier functions

20. Genetic Disorders

21. Pedigree Analysis

22. Pedigree Analysis