Genetics

1. Genetics

2. TAKS and TEKS Objectives Objective 2: Understanding of living systems. (6) Student knows the structures and functions of nucleic acids in the mechanisms of genetics. (D) compare genetic variations observed in plants and animals.

3. Alleles • Genes-are sections of DNA on a cell’s chromosomes that controls traits • Genes exist in alternative (different) forms or alleles. Example: (BB, Bb, bb) • Alleles are found on different copies of a chromosome (1 inherited from mom and the other from dad)

5. Homozygous vs. Heterozygous • Organism is Homozygous for a trait if its two alleles for the trait are the same • Ex. TT, aa, GG, tt Remember: Homozygous = the same • Organism is Heterozygous for a trait if its two alleles for the trait are different • Ex. Tt, Aa, Gg, Remember: Heterozygous = different

7. Dominant vs. Recessive Traits • Traits-are characteristics that are inherited from one generation to the next • If organism is heterozygous for a trait, only 1 form of the trait will be observed. The observed trait is dominant. The masked (covered) trait is recessive.

8. This rabbit has the dominant trait for white hair color

9. Phenotypes vs. Genotypes • A parent randomly passes only one allele (gene) for each trait to each offspring • Two organisms can look alike but have different genetic combinations • Phenotype-describes how an organism looks (physical appearance) (Example: brown eyes, blue eyes, green eyes, tall or short) • Genotype-is the gene combination an organism has (genetic makeup) (GG, Gg, gg)

10. Phenotypes Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes.

11. Punnett Square • The probability or the outcome of a cross is determined by doing a Punnett Square. • If the parent genotypes are known, a Punnett Square can be done to calculate the possible genotypes of the offspring. • In a Punnett Square, Dominant Allele--(strong gene)—is represented by any capital letter—for example: B, G, T • The same lower case letter represents the Recessive Allele for example: b, g, t

12. Punnett Square Practice T=Tall Plant (Dominant) t=short plant (recessive) • If we cross two tall plants, each with Tt genotype, what would happen? Answer Heterozygous tall plant Tt Parental Allele t T TT T Tt Heterozygous tall plant T t Tt tt t Parental Allele

13. Monohybrid vs. Dihybrid • Two types of Punnett Squares are: • *Monohybrid Square—we only cross one trait. The prefix Mono means “one” • *Dihybrid Square—we cross two traits. Prefix Di means “Two”

14. Complex Patterns of Inheritance • Simple Inheritance-is controlled by dominant and recessive paired alleles (genes TT, Tt, tt) • Complicated Inheritance-most alleles (genes) are not simply dominant or recessive • Complicated Inheritance Patterns include: • Incomplete Dominance • Codominance • Multiple Alleles

15. Incomplete Dominance • The phenotype (appearance) of the offspring is intermediate between those of the two homozygotes because neither allele of the pair is completely dominant Example Homozygous White Flower Homozygous Red Flower All 1st Generation Offspring Pink Flower X =

16. Codominance • Both alleles (genes) are expressed equally crossed with • For example: Type A Blood X Type B Blood = ABBlood

17. Multiple Alleles • More than two alleles often control a trait in a population. • For example, four alleles (genes) of a single gene– C,cch,ch, and c—govern color coat in rabbits • The dominant C allele produces a gray coat • The cch allele results in a light gray coat. This allele is dominant to the ch and c alleles • The challele results in a white coat with black markings • The c allele produces a pure white coat

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29. Let's have a short Review

30. Genetics – How traits are inherited • Father of Genetics is Gregor Mendel, he experimented with pea plants. • Dominant traits always are visible, and are represented by capital letters. • Recessive traits are hidden unless both alleles are the recessive one (Homozygous) • At least one pair of alleles determines the trait in genetic inheritance.

31. Punnett Squares d d D Dd Dd d dd dd Heterzygous & Homozygous Recessive Heterzygous & Heterozygous D d D DD Dd d Dd dd • D d • D DD Dd • D DD Dd D D d Dd Dd d Dd Dd Homozygous Dominant & Heterozygous Homozygous Recessive & Homozygous Dominant

32. Phenotype is what you see • Phenotype refers to what is visible – the dominant trait or the recessive trait. • How do you know the phenotype? • LOOK!!

33. Genotype – actual combination of alleles • Only 3 possibilities • BB = Homozygous Dominant • Bb = Heterozygous • bb = Homozygous recessive • Must look at inheritance pattern to find out.

34. Pedigree shows the Family Tree Parents: Father has; Mother is a Carrier

35. Answer • 3 / 4 of the offspring are Tall T=Tall, and 1 / 4 of the offspring are short t=short; this is the offspring’s phenotype • Phenotype-describes physical appearance (Tall, short) of offspring. We always look at the first letter only of the square to know its appearance • Of the tall (T) offspring: 1/ 3 will be homozygous dominant (TT) and 2 / 3 will be heterozygous (Tt) • The genotype ratio (look at both letters) for this cross is 1 TT: 2Tt: 1 tt; the phenotype ratio is 3 tall: 1 short