Patterns of Inheritance

Transcription

1 Patterns of Inheritance

2 Mendel the monk studied inheritance keys to his success: he picked pea plants he focused on easily categorized traits he used true-breeding populations parents always produced offspring with the same traits as the parents he tested 29,000 plants!!! he apparently had lots of time.

3 Mendel s experiment He first repeatedly bred together similar plants until he had distinct populations, each the same for a particular trait; called them true-breeding.

4 Mendel s experiment 1) Cross true-breeding parent plants that differ in only one trait 2) Let the offspring self-fertilize 3) Collect and analyze results from 1 st and 2 nd generations.

5 Results of monohybrid cross Where did the white flower come from?!

6 Mendel s conclusions Alternate versions of instructions account for variability of inherited traits Each parent puts a set of genes in every sperm or egg Offspring receive 2 copies of genes, one from each parent if both alleles are the same = homozygous if alleles are different = heterozygous -zygous, suffix meaning "having zygotes of a specified kind zygote means yoked (joined)

7 What do you think the genotype of Mendel s true breeding populations was?

8 Mendel s conclusions If the two alleles are different, the one that determines the organism s appearance is called dominant; the one without any noticeable effect is called recessive genotype determines phenotype

9 Genotype determines phenotype: the only way a recessive trait is expressed is when there are two copies of it

10 What are the two alleles inherited by offspring carried on?

11 Homologous chromosomes

12 Regarding the dominant allele... It does not mean it is bigger or stronger than the recessive allele It does not mean more numerous in the population It does not mean it is the more desirable or better allele It just means it is the one that determines the organism s appearance

13 Polydactyly-dominant allele

14 Types of inheritance Complete dominance Incomplete dominance Codominance Polygenic Pleiotropy Sex-linked

15 Complete dominance When the dominant allele has the same effect on phenotype whether present in one copy or two When the offspring looks like one of the two parents This was Mendel s conclusion

16 Incomplete dominance When neither allele is completely dominant Phenotype of the heterozygote differs from the two homozygous varieties It has an intermediate phenotype; it does not look like either parent

17 Codominance When a heterozygote fully expresses both alleles Example: AB blood type

18 Polygenic inheritance Multigene traits; the additive effects of two or more genes on a single phenotypic character ex: skin color, eye color, hair color, height

19 Pleiotropy Single gene can influence multiple unrelated traits Most genes act this way the gene may code for a product that is used by various cells, or has a signaling function on many cells

20 Sex-linked inheritance A gene located on either sex chromosome Historically, the term sex-linked refers to genes on the X chromosome X chromosome is relatively large & carries genetic information about many nonsex-related traits There is no essential genetic information carried on the Y chromosome Sex-linked traits differ in their patterns of expression in males & females

21 Sex-linked disorders Affect mostly males, XY Because females are XX, if a disorder is on one X chromosome, the female has a spare X chromosome to keep her phenotype normal. Because males have only one X chromosome, the male will express that trait (whether it is defective or not). examples: hemophilia, color blindness

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23 Autosomal disorders Recessive disorders result from heterozygote matings; the parents are both carriers for that allele ex: cystic fibrosis Dominant disorders heterozygotes are not carriers; why not? 50% of offspring will inherit disorder ex: Huntington s disease

24 Why is what the doctor said wrong?

25 Characteristics studied by Mendel

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27 What kind of inheritance is this?

28 How many alleles does each person have per gene? How many alleles can there be in a population?