CHAPTER 7 Extending Mendelian Genetics Section 7 1

CHAPTER 7 Extending Mendelian Genetics

Section 7. 1: CHROMOSOMES AND PHENOTYPE KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

gene

KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. 2 Genes for characteristics not directly related to sex. 1 Directly controls development of sex characteristics

Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture.

• Mendel’s rules of inheritance apply to autosomal genetic disorders. - - A heterozygote for a recessive disorder is a carrier 支架. A carrier does not show symptoms of disease but can pass it on to offspring Disorders caused by dominant alleles are uncommon. (dominant)

• Mendel’s rules of inheritance apply to autosomal genetic disorders. Autosomal Recessive D d Autosomal Dominant D d DD Dd D no disorder carrier disorder Dd dd disorder no disorder carrier disorder d

Males and females can differ in sexlinked traits. • Genes on sex chromosomes are called sex-linked 4 genes 性关联基因. 6 – Y chromosome genes in mammals are responsible for male characteristics. – X chromosome genes in mammals affect many traits.

• 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.

• 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.

Section 7. 2: COMPLEX PATTERNS OF INHERITANCE KEY CONCEPT Phenotype is affected by many different factors.

Complete Dominance RED (dominant) X WHITE (recessive) --- RED

Phenotype can depend on interactions of alleles. • In incomplete dominance 不完全统治, neither allele is completely dominant nor completely recessive. – Heterozygous phenotype is intermediate between the two homozygous phenotypes; mixture – Homozygous parental phenotypes not seen in F 1 offspring

INCOMPLETE DOMINANCE RED X WHITE --- PINK

• Codominant 共显性 alleles will both be completely expressed. – Codominant alleles are neither dominant nor recessive. – patches, strips, spots

• Codominant 共显性 alleles will both be completely expressed. – Codominant alleles are neither dominant nor recessive. – The ABO blood types result from codominant alleles. 3 • Many genes have more than two alleles. - multiple allele trait - Example- blood type

CODOMINANCE RED X WHITE --- RED and WHITE spots, patches, stripes

Many genes may interact to produce one trait. • Polygenic 多基因 SG traits are produced by two or more genes. Order of dominance: brown > green > blue.

• An epistatic gene 上位基因 can interfere with other genes.

• An epistatic gene can interfere with other genes.

8 9 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 • warmer – female • cooler - males • Height is an example of a phenotype strongly affected by the environment.

Section 7. 3: GENE LINKAGE AND MAPPING KEY CONCEPT Genes can be mapped to specific locations on chromosomes.

Gene linkage was explained through fruit flies. • Gene linkage: 1 – Certain traits are inherited together 2 – Fruit flies useful because can be grown cheaply and quickly. Wild type Mutant

4 Gene linkage was explained through fruit flies. • Morgan found that linked traits are on the same chromosome. • Chromosomes, not genes, assort independently during meiosis. Mutant Wild type 3 • • • Red eyes Wings Brown Body • • • White eyes No wings Different body color

Mendel: Genes assort independently of one another.

Punnett, Bateson: • Some genes are linked, so those genes are often inherited together.

Morgan: • Linked genes are not inherited together every time. • Chromosomes exchange homologous genes during meiosis.

5 • 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 6 between genes. • Linkage maps show the relative locations of genes. 7

• 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

• The higher the crossover frequency, the farther the genes 8 are on a linkage map. • Linkage maps show the order and relative position of 9 genes on a chromosomes

Linkage Map A-C: 25% A D 7% B C 13% 5%

Section 7. 4: HUMAN GENETICS AND PEDIGREES KEY CONCEPT A combination of methods is used to study human genetics.

Human genetics follows the patterns seen in other organisms. • The basic principles of genetics are the same in all sexually reproducing organisms. 1 – Each offspring • ½ chromosomes from mother • ½ chromosomes from father – Inheritance of many human traits is complex. – Single-gene traits are important in understanding human genetics. 2 • Easy to find out which traits are • dominant and which are recessive

Females can carry sex-linked genetic disorders. • Males (XY) express all of their sex linked genes. 4 – Most on X chromosomes – No 2 nd X to mask the allele in males • Expression of the disorder depends on which parent carries the allele and the sex of the child. Y X

Females can carry sex-linked genetic • Males (XY) expressdisorders. all of their sex linked genes. • Expression of the disorder depends on which parent carries the allele and the sex of the child. Y- linked EAR HAIR Y X

5 6 A pedigree 谱系 is a chart for tracing genes a family. • Phenotypes are used toininfer genotypes on a pedigree. • Autosomal genes show different patterns on a pedigree than sex-linked genes.

7 • If the phenotype is more common in males, the gene is likely sex-linked.

SEX-LINKED

AUTOSOMAL DOMINANT

AUTOSOMAL DOMINANT

SEX-LINKED

AUTOSOMAL RECESSIVE

AUTOSOMAL DOMINANT

AUTOSOMAL RECESSIVE

9 • Several methods help map human chromosomes. A karyotype 核型 is a picture of all chromosomes in a cell. XY

• 10 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 11. Picture of all ______ in the cell

1. 2. 3. 4. 5. CHAPTER 7 Study Guide Cytogenetics Report Mendelian Genetics “Exceptions Sex-linked Traits Human Pedigrees Your 11. 3 and 11. 4 Practice grade will be included in this packet as well