GeneticsLab 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 letterRecessive – 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: F1Next generation: Filial 2: F2

And so on

F1 OffspringPP- homozygous dominant = purplePp – heterozygous - purplepp – homozygous recessive = white

Example: page 191: Parents: PP and ppGametes: P from purple-flowered parent p from the white-flowered

parentOffspring: genotype: PpPhenotype: 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 kid50% 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- dominant p – 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 199 - 200

Researchers cannot control crosses in humans as they do in plants like Mendel did.

Geneticists study crosses that have been performed alreadyFamily 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 (-) (+)