Genetics Lab 11

The Family

The Principles of Mendel  Experiments in Plant Hybridization” – scientific paper written in 1866 by Gregor Mendel  Went unnoticed until closer to 1900 –  Mendel’s findings: Foundation of Mendelian Genetics  Main idea: dismiss blending theory with Particulate theory

Particulate Theory  States:  Inherited characters are determined by particular factors (now called genes)  These factors occur in pairs (genes occur on maternal & paternal homologous chromosomes)  When gametes form, these genes segregate so that only one of the homologous pair is contained in a particular gamete. (remember meosis?)

This theory ….  Is known as “ The Law of Segregation” (first law)  His second law: “The Law of Independent Assortment” states: that genes on nonhomologous or different chromosomes will be distributed randomly into gametes.

Vocabulary  Gene – a unit of heredity on a chromosome  Alleles – alternate states of genes; contributed to an organism from its parent. Alleles for a particular gene occur in pairs.  Dominant – alleles that mask expression of other alleles; capital letter  Recessive – alleles whose expression is masked; lower case letter

Genotype & Phenotype  Genotype: All the alleles of an organism present in a cell (dominant or recessive)  Phenotype: The physical appearance of a trait.

Homozygous  When paired alleles are identical:  PP, pp, GG, gg, II, ii

Heterozygous  Pairs of different alleles: Pp, Ii, Bb

Simple Dominance

Generations  Parental generation “P”  First generation: Filial 1: F1  Next generation: Filial 2: F2  And so on

F1 Offspring PP- homozygous dominant = purple Pp – heterozygous - purple pp – homozygous recessive = white  Example: page 191:  Parents: PP and pp  Gametes: P from purple-flowered parent  p from the white-flowered parent  Offspring: genotype: Pp  Phenotype: purple

What is the ratio of purple-flowered (PP or Pp) to white flowered (pp) offspring?

Answer  Genotypic ratio of F1 generation:  1 PP : 2 Pp : 1 pp  Phenotypic ratio of F1 generation:  3 purple : 1 white

Procedure 17.2  Albinos – homozygous recessive (aa)  Suppose a woman having normal colored skin and an albino mother marries an albino man:

Normal mom & Albino dad  Genotype of children’s mother: _________________  Genotype of children’s father: _________________  Possible gametes of mother: _________________  Possible gametes of father: _________________  Genotype ratio of children: _________________  Phenotype ratio of children: __________________

Answer:  50 % chance of albino kid  50% chance of normal kid

Procedure 17.2  Color ratio for corn plants  Will not do height  corn did not cooperate  Colors will be purple and yellowy-white ( not red and white)  P- dominantp – recessive  PP – purple  Pp-purple  Pp – yellowy white

Corn Parents: PP and Pp  F1 = all Pp  F2 = ?  Pp x Pp  3 purple : 1 white  3: 1 phenotypic ratio

Activity  Work in your groups: 1 reader, 3 recorders  Read down the corn and give “tic” marks for every purple and “tic” mark in separate column for yellowy-white kernels.  Do for about 200 kernels  See if ratio is as it should be  Ex: 160/40 = 4 40/40 = 1

Incomplete Dominance  In this type of inheritance, the heterozygous genotype results in an “intermediate” characteristic  Ex: Red flower – RR crossed with white flower –rr  Parents: RR (red) x white (rr)  Gametes: R r  Offspring: Rr = pink

Lethal Inheritance  Involves the inheriting of a gene that kills the offspring.  Ex: Huntington’s Disease – slow manifestation so offspring generally reproduce before they know they have it.  We will discuss more shortly

Other Sources of Genetic Diversity  Multiple alleles  Gene interaction (epistasis)  Continuous variation  Environmental effects  Linkage  Sex linkage

Sex-linkage  Color-blindedness (color deficiency)  Inability or decreased ability to see color, or perceive color differences under normal lighting conditions.  The genes that produce photopigments are carried on the X chromosome  If some of these genes are missing or damaged: color blindness will be expressed in males with a higher probability than females because males only have on x chromosome.

Remember: Autosomes Sex determining chromosomes (XX, XY) X = about 1500 genes Y = gene poor: 78 genes Colorblindness: recessive mutation on x chromosomes Hemophilia: mutations on x chromosome

Hemophilia hemophilia - recessive X chromosome mutations  So both x chromosomes have to have a hemophilia mutation to have hemophilia (phenotype)  XX^h = mom a carrier ; no hemophilia  X^h X^h – mom Does have hemophilia  For man to have this phenotype – only needs on one x chromosome he has : X^hY – has hemophilia  Who more likely to have? Male or female?  Female needs 2 (1/7000 x 1/7000 = 1/49,000,000), men need on one (1 in 7000)

Other Human Traits  Page 197

Analyzing Pedigrees page  Researchers cannot control crosses in humans as they do in plants like Mendel did.  Geneticists study crosses that have been performed already  Family histories

Pedigrees  A consistent graphical presentation of mating's and offspring over multiple generations for a particular trait  Geneticists deduce the mode of inheritance of a trait  See table 17.4 on page 199

Page 200  Symbols  Procedure 17.5

17.3 – page 196: Determine Blood Type for ABO system  We will not work with synthetic blood  Terminology:  Blood Types: A, B, AB, O  Blood Group Genes: I^A I^B i  Rh  (-) and (+) (D gene)  Dd OR Dd = Rh positive (dominant)  dd = Rh negative (-) (recessive)

Agglutination  Clumping. NOT clotting  Occurs when blood mixed with an antiserum  Indicates the presence of a the respective antigen on rbc’s

continued  Blood Group  A  anti b in plasma ( naturally occurring antibodies)  B  anti b in plasma  AB  no anti a or anti b  O  has both anti a and anti b

A B AB O Rh (-) (+)