Science 3 / Ch. 10

CHAPTER 10- Mendel and Meiosis…GENTICS

Gregor Mendel- - Austrian Monk who discovered how to raise certain types of pea plants - first person to succeed in predicting how traits would be transferred from one generation to the next

P1 genteration- parent generation F1 generation – offspring from the P1 generation F2 generation- offspring from the F1 generation

Monohybrid cross- (mono = 1) (hybrid = 1 of each)…Mendel crossed a pure tall pea plant with a pure short pea plant

Allele- the alternative form of a gene…represented by letters (T = tall, t = short)

Dominant- a trait that you will observe Recessive- a trait that will be covered up by the dominant one

Homozygous- (homo = same) – has 2 dominant alleles or 2 recessive alleles

Heterozygous- (hetero = one of each) – has one of each trait…the dominant one will always show up.

Law of Segregration – a random combination of alleles 2 alleles for each trait, a parent passes on an allele at random

Phenotypes and Genotypes - the way an organism looks and behaves is its PHENOTYPE o the phenotype of a tall pea plant is “tall” whether it has TT or Tt o Phenotype Ratio- will be presented as a percent with the phenotype…EX: 75% tall, 25% short

- the gene combination an organism contains is known as its GENOTYPE o “TT” or “Tt” o Genotype Ratio – will be presented as percents with the alleles…EX; TT- 50%, Tt – 25%, tt – 25%

• • • you can’t always know the genotype by looking at the phenotype***

Dihybrid Crosses

- when Mendel crossed plants that had 2 (di) traits that differed …used seed shape and color

Law of Independent Assortment Genes for different traits are inherited independently of each other

Ex: when a pea plant with the genotype RrYy produces gametes, the alleles R and r will separate (law of segregation) as well as from the alleles Y and y (the law of independent assortment) and vice versa -the alleles will recombine in 4 different ways

• • if the alleles for seed shape and color were inherited together (RY & ry) only 2 types of pea seeds would have been produced: Round Yellow and wrinkled green

Homologous chromosomes- -two chromosomes of each pair in a diploid cell helps determine what the individual organism looks like. -each pair of homologous chromosomes has genes for the same trait

DIHYBRID CROSS

R- Round (dominant) r- wrinkled (recessive) Y- Yellow (dominant) y- green (recessive)

P1- RRYY x rryy RY x ry (what each plant gives off)

F1- RrYy –all round & yellow F2- RrYy x RrYy (Mendel let the F1 generation plants cross pollinate) - need to figure out all the possible combinations RrYy:(you distribute) RY, Ry, rY, ry - for the Punnent Square, you need 16 boxes

Possible Phenotypes from this Punnent Square 1. Round Yellow 2. Round Green 3. Wrinkled Yellow 4. wrinkled green - need to find the genotypes that go with the phenotypes

Practice this Punnent Square. Include the Phenotype and Genotype ratios.

TR Tr tR tr Phenotype Ratio TR 1. /16 2. /16 Tr 3. /16 4. /16 tR Genotypes Tr

Try to cross these two parents… TtRr x ttRr (**hint** there won’t be as many combinations as in th one above)

10-4-06 Meiosis: Sometimes there is a mistake and would not separate, so one side would be a blank and the other would get the extra chromosomes When mistakes happen during the separating…called nondisjunction

Trisomy: when #21 chromosome is fertilized by a normal gamete, the resulting zygote has 47 instead of 46 chromosomes…resulting in Down Syndrome Monosomy: when a gamete with a missing chromosome fuses with a normal gamete during fertilization, the resulting zygote lacks a chromosome…resulting in usually death (zygote doesn’t develop)…Turner Syndrome can result when the zygote and organism do survive…(a female will only have a single X chromosome) Triploidy: involves a lack of separation of homologous chromosomes… the gamete inherits a complete diploid set of chromosomes…when this gamete is fertilized by a normal gamete, the offspring has three sets of chromosomes and is triploid…if these 2 fuse then a tetraploid Polyploidy: organisms with more than the usual number of chromosome sets…rare in animals and almost always results in death of the zygote…polyploidy is common in plants and allows many different kinds of plants.