Genetics Unit Review

1. Genetics Unit Review

2. Concept Overview (this is online) • 1.         Mitosis • 2.         Cell cycle • 3.         Meiosis •             a.         Be sure that you can compare the two processes •             b.         Spermatogenesis, oogenesis •             c.         Fertilization • 5.         Mendel •             a.         Importance of his work •             b.         3 Mendelian principles •                         i.         Segregation, dominance, independent assortment • 6.         Probability • 7.         Single Trait Crosses, 2 trait crosses • 8.         Lethal alleles • 9.         Incomplete and Codominance •             a.         Blood genetics • 10.       X linked • 11.       Pedigrees •             a.         Autosomal dominant, autosomal recessive, X-linked • 12.       Karyotypes                  • 13.       Polygenetics • 14.       Pleiotropy • 15.       Disorders associated with Genetics •             a.         Non disjunctions •             b.         Klinefelter, Turner, Down’s, XXX, XYY

3. You should not write down everything you see in the following slides as you’ve seen it all before … be sure to get through the entire presentation by the end – there are a couple of hints

4. What is the difference between mitosis and meiosis? (you should already know this)

5. What are the sources of Genetic Variation in Meiosis? • Crossing Over – crossing over of genetic information of homologous chromosomes during prophase I • Independent Assortment – random alignment of maternal/paternal chromosomes during metaphase I • Fertilization - two gametes (sex cells) coming together to form a zygote

6. How are sex cells produced? Spermatogenesis – formation of male gametes that are specially designed for movement Oogenesis – cytoplasm of female gametes does not divide equally – one daughter cell receives most of the cytoplasm  1 egg and 3 polar bodies

7. How is sex determined? • Sex chromosomes – one pair of chromosomes that have a role in the sex of an individual • Autosomes – not sex chromosomes (we have 22 pairs of these)

8. How does a nondisjunction occur in meiosis? (important!) Nondisjunction – two homologous chromosomes move to the same pole during meiosis either too much or not enough genetic info. http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ge/m3/s3/index.htm • Monosomy – missing 1 chromosome (2n=45) • Trisomy – 1 extra chromosome (2n=47) • **Be sure to be familiar with Klinefelter’s, Turner’s, Down’s, XXX, XYY and what causes them Down Syndrome 3 chromosome 21 Turner’s Syndrome - 1 X

9. How can a karyotype chart be read?

10. What are Mendel’s laws? • Inherited characteristics occur in pairs – each member of the pair is an allele • An allele can mask the expression of another allele – 1) principal of dominance • dominant allele – uppercase letter • Recessive allele – lowercase letter • 2) law of segregation - Alleles separate/ segregate during meiosis • 3) Law of independent assortment – each allele is independent and is assorted independently during gamete formation

11. What are the various crosses we have done? (you may want to write this – it’s a summary) • Single trait (Ex: HH x hh) • Monohybrid (Hh x Hh) – both parents are heterozygous – can apply Mendel’s 3:1 ratio for phenotype only in this situation • Two trait crosses (Ex:DDrr x ddRR) • Dihybrid (DdRr x DdRr) - both parents are heterozygous for both traits– can apply Mendel’s 9:3:3:1 ratio for phenotype only in this situation • Codominance – 2 alleles equally dominant – the phenotype for heterozygote displays both alleles (ex: red&white flowers, Blood type AB) • Incomplete Dominance - 2 alleles equally dominant – the phenotype for heterozygote displays new phenotype (ex: pink flowers) • X-linked

12. P – GGrr x GgRr 1)List the possible gametes for each parent – use FOIL GGrr – Gr, Gr, Gr, Gr GgRr – GR, Gr, gR, gr 2) The gametes for one parent are written across the top and the gametes for the other parent are written down the side How do you find the gametes in a dihybrid cross? GR Gr gR gr F1 Notice that the genotypes in this row repeat in the next 3 rows… Gr Gr Gr Gr

13. What is Pleiotropy? So far we have only considered genes that affect a single phenotypic character it is more common that one gene can have multiple effects Pleiotropy A gene that affects more than 1 phenotype individuals lack pigment in their skin and hair, and also have crossed eyes at a higher frequency than pigmented individuals

14. What is Polygenics? More than 1 gene controls a particular phenotype In this simplified example of skin colour – we have 3 genes (A, B, C) controlling skin colour • These traits range across a continuum • Weight • Height • Skin colour, hair colour, eye colour

15. Dominant Pedigree • Used to represent disorders that are carried by the autosomes. • If the identified allele is present then the trait will be expressed. • filled symbols represent individuals (men and women) with the trait or disorder.

17. Recessive Pedigree • used to represent disorders that are carried by the autosomes. • inherited as a recessive trait. • no dominant alleles present. • Since it is expressed as a recessive trait, you know exactly what the genotype is for affected individuals.

19. X – linked Pedigree • the two previous example pedigrees we studied were both autosomal. • This means that the disorder did not depend on the gender of the individuals. • Some disorders that are caused by defective sex chromosomes.

21. Be sure to do some of the questions online and in your textbook • Also review your quizzes