Name:________________________ Per:______ Teacher:_____________

Biology- Unit #6 – Basic Genetics

Essential Skills

• Be able to show the expected phenotype and genotype ratios for any single trait Punnett Square cross.

• Recognize the terms genotype, phenotype, dominant, recessive, heterozygous and homozygous.

• Use a pedigree to determine the probable mode of inheritance of a trait.

Study Guide

1. How do we represent a dominant allele? Recessive? 2. Using the letter “T” for the allele, write an example of homozygous dominant, homozygous recessive, and

heterozygous individuals. 3. Explain how the following terms relate to each other:

a. DNA – Chromosome b. Gene – Chromosome

c. Gene – Trait d. Trait – Allele

4. What is the Law of Segregation? 5. How is the Law of Segregation related to Law of Independent Assortment? 6. Explain the purpose of Meiosis. How many cells? Types of cells? Chromosome Number? 7. Draw a picture of Crossing-over. Show the alleles on different chromatids and the new combinations of genes produced. 8. Compare and contrast the following sets of terms: * Dominant vs. Recessive – * Genotype vs. Phenotype – * Homozygous vs. Heterozygous – * Purebred vs. Hybrid - 9. How does genotype affect phenotype? Use the terms dominant, recessive, homozygous and heterozygous. 10. If short tails are dominant to long tails, what are the phenotypic and genotypic ratios of a cross between a dog

with a long tail and a dog with a short tail (who had a parent with a long tail)? 11. If you had a long tailed dog and did not know the phenotypes of its parents, how could you conclusively

determine the genotype of your dog? Explain using examples of a Test Cross.

12. Complete the following table that summarizes the 4 basic genetic crosses: (B=black; b =brown)

in capital letters; in lower case letters

TT, tt, Tt

dna is found in chromosomes

genes are segments of chromosomes (homologous)

a trait is determined by a gene

a pair of alleles make up a gene, which in turn code for a trait

when chromosomes get separated during Anaphase I of Meiosis

After segregation, chromosomes migrate rrandomly to different gametes

dominant alleles hide recessive ones

a genotype determines the phenotype

same size letters in a gene; different size letters

heterozygous are hybrid, homozygous are pure

Genotypes determine phenotypes. They can contain dominant traits in homozygous or heterozygous forms, recessive traits are only expressed in homozygous recessive genotypes

assuming short tail is homozygous dominant: 100% short tail in offspring

make a punnett square using parents whoare homozygous recessive

Word Cross Genotype Cross Offspring Genotype Ratio Offspring Phenotype Ratio

BB x bb

Homozygous Dominant x Heterozygous

1 BB: 2 Bb: 1 bb

2 Black : 2 Brown

13. How are Incomplete Dominance and Co-dominance similar? How are they different from each other? Give examples of each type of inheritance. 14. Differentiate between a multiple allele trait versus a trait that is determined by incomplete dominance . Give examples of each type of inheritance. 15. Show the expected genotype and phenotype ratios of a cross between a man with type A blood and a woman with type B blood (both the man and woman had parents with type O blood). 16. What is the difference between Autosomes and Sex Chromosomes? What sex chromosomes determine male? Female? Why do sex-linked traits affect males more than females? 17. Show the expected genotype and phenotype ratios of a cross between a man who is colorblind and a woman who has normal vision (but her father was colorblind). 18. A woman has hemophilia. What are the genotypes of her parents? Using a Punnett Square, show the cross that results in the woman inheriting hemophilia. 19. Pedigrees:

20. In a pedigree, what do the circles represent? Squares represent? What does it mean if a circle or square is completely shaded? What does it mean if it is only half-shaded? What if there is no shading?

a. Is this pedigree showing a dominant or recessive disorder? b. How do you know? c. Write all possible genotypes for individuals shown on the pedigree.

Homozyg. Dom X hom recessive

BB X Bb

Both are only visible in Heterozygous genotype. Incomplete: a mix of parental traitscodominance: parental traits are expressed without mixing in same indiv.

multiple alleles: blood type. Incomplete dominance: mix of parental traits.

25% AO, 25% BO, 25% OO; 25% AB

autosomes: any non-sex chromosome. males: XY, femalesXX. Males can't be carriers

25% female colorblind, 25% normal females; 25% normal males, 25% colorblind males

hemophilia is recessive. If parents are normal, then both are heterozygous.

dominant

individual 6 is affected

circles: femalessquares: malesshaded shapes: affectedhalf shaded: carriersno shading: normal

Aa aa

Aa Aa aa aaAa

Aa

aa aa

aa aa aa aa

aa

2BB : 2Bb 4:4 black

4:4 Bb 4:4 Black

heterozygous X heterozygous Bb X Bb 3 black: 1 brown

Bb X bbhetero X homo recessive 2Bb : 2 bb