Sexual Reproduction Part 2: Genetics

Transcription

1 Sexual Reproduction Part 2: Genetics Describe possible allele combinations in an egg or sperm cell given a combination of two traits and a parent s genotype for the two traits. Describe the possible combinations of offspring in a simple Mendelian genetic cross for two traits. Describe the possible combinations of offspring in a genetic cross involving co- dominance or incomplete dominance for a single trait.

2 Stand Up Please Please stand near the door if you can roll your tongue Clasp your hands together if your right hand is on top stand near the door Form a line, with (naturally) light hair closest to the door and dark hair closest to the periodic table. Form a line, with blue eyes near the door and brown eyes closest to the periodic table.

3 Reflection Questions These are all examples of TRAITS, coded for by GENES in DNA. Were the same people always together? Do any of these traits appear to be linked?

4 Assignment Read section 9-1 The Work of Gregor Mendel on pages Define the bold words in your notebook. Answer the section review questions (p. 189) in your notebook. When you finish, continue with sections 9-2 & 9-3.

5 10/30/2013 Do Now: Being double jointed is caused by a recessive gene. If one parent is double jointed, and the other parent is not double jointed but carries the gene for it, what are the odds their children will be double jointed? Agenda: Notes and Finish Bookwork from Monday Take out your bookwork from Monday for me to review, please

6 Introduction to Genetics Gene Segment of DNA that codes for a protein/trait Trait A characteristic of a living thing determined by it s genes (DNA) Chromosome Coiled DNA strand that looks like an X or a Y during cell division.

7 Punnett Square Father (Brown) B b Mother (Brown) B BB (Brown) bb (Brown) b Bb (Brown) bb (blue) Make your own Punnett Square for some combination of blue and brown eye alleles. * Disclaimer: This is how classical Mendelian Inheritance works. Most human traits are not this simple, eye color included.

8 Gender Gender in humans is determined by the X and Y chromosomes. Mother X Father X XX (girl) Y YX (boy) X XX (girl) YX (boy)

9 Sex-Linked Traits Some traits are more common in males than females because the Y chromosome is much smaller, and does not have copies of many genes. Mother Father Color vision (Carrier for color blindness) X V Y X V X V X V (color) Y X V (color) X v X V X v (color) YX v (color blind)

10 Gregor Mendel Mendel s laws A monk born in the Czech Republic in He is credited with discovering basic genetics by studying pea plants. Mendel s Law of Segregation: alleles of genes separate when gametes are formed. Independent Assortment: Chromosomes separate independently of one another in the formation of gametes

11 11/4 (2 nd period) 11/5 (4 th period) Do Now: The gene for brown (B) eyes is dominant over the gene for blue (b) eyes. If a woman and man with brown eyes and the alleles Bb have children, is it possible for any of their children to have blue eyes? What is the probability a child of theirs will have blue eyes? Agenda: Finish Bookwork/vocab from last week Take out your bookwork from Monday for me to review, please

12 Vocab you should have Gene Trait Chromosome Alleles Dominant Recessive Genotype Phenotype If you are done with Vocab: Check that you are done with Questions 1-5 on Page 189 Questions 1-4 on Page 192 Questions 1-5 on Page 196 If done with all, ask me to check your work Homozygous (BB or bb) Heterozygous (Bb) Sex-linked trait

13 Questions from Elephant Book Page 189 If you did not finish in class, perhaps you can find answers to these questions online Page 196 Page 192

14 Alleles (ex: blue eyes and Brown eyes) Different forms of the same gene. Dominant (ex: Brown eyes) A form of a gene that is expressed even when another form is present. Recessive (ex: blue eyes) A form of a gene that is only expressed when both alleles are the same.

15 Genotype (Bb) The genetic characteristics or DNA code of an organism Phenotype (brown eyes) The physical characteristics of an organism Homozygous (BB) When both alleles of a gene in an individual are the same. Heterozygous (Bb) When the alleles are different.

16 Sex-linked trait: A trait genetically determined by an allele located on the sex chromosome (X or Y). Most sexlinked traits are on the X chromosome and affect males much more than females.

17 11/6 (2 nd period) 11/7 (4 th period) Do Now: The gene for brown (B) eyes is dominant over the gene for blue (b) eyes. If a woman (Bb) and a man (Bb) have children, what is the genotypic ratio for this cross? The phenotypic ratio? Agenda: Finish checking bookwork; talk about crosses and ratios Take out your notebooks

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19 Linkage and Crossing Over You may have noticed that people with dark hair generally have dark eyes. This is because the genes for these traits are on the same chromosome. Some traits are linked (like eye color & hair color), because they are on the same chromosome (ex. Black hair and brown eyes) However, some people do have blue eyes and black hair. This is generally because of crossing over. But crossing over of homologous chromosomes can cause these traits to become unlinked (ex. Black hair and blue eyes)

20 Mutations Sometimes unexpected things happen A mutation is a change in the DNA There are several possible explanations: Damage to the DNA occurs during replication Molecular decay Mutagens cause change Other unknown factors Mutations can cause disease, be meaningless or be beneficial