CHAPTER 7 KEY TERMS GeneticsPurebred CrossHybrid DominantRecessive PhenotypeGenotype GameteCarrier Inherited DisorderSex-Linked Trait RegenerationCodominance

CHAPTER 7 GENETICS OF ORGANISMS

ORIGIN OF MODERN GENETICS Genetics Study of the inheritance of traits Gregor Mendel Roman Catholic monk who was very interested in science Experimented with pea plants The traits that he observed could have 2 variations 3

ORIGIN OF MODERN GENETICS Purebred Organisms that pass on the same traits over many generations Ex. tall pea plants Mendel mated purebred plants of opposite traits to see what the outcome would be Mated purebred tall plants with purebred short plants Cross Mating organisms with specific traits Hybrid The offspring of unlike parents (one parent was tall, one was short) 4

ORIGIN OF MODERN GENETICS Parent generation F 1 generation F 2 generation Noticed that even though both F1 plants were tall, when bred together, they produced some offspring that were short After carefully studying his data, he proposed some theories to help explain what he was observing 5

ORIGIN OF MODERN GENETICS Mendel proposed that each organism has 2 factors that determine which trait is shown Each factor comes from one of the parents If both factors were the same = purebred If factors were different = hybrid Another theory suggested that each factor was either dominant or recessive Dominant has more influence on the trait Recessive has less influence on trait 6

GENETICS We use letters to describe the trait Dominant traits are capitalized while recessive traits are lowercase Dominant tall trait = T Recessive short trait = t Homozygous Contains 2 of the same letters (TT, or tt) Heterozygous Contains 1 dominant and 1 recessive (Tt) 7

GENETICS Genotype The factors an organism possesses Phenotype The appearance of the organism 8 Zygote Cell formed from 2 parent cells His work went unnoticed for about 50 years

GENES Genes are located on chromosomes The number of chromosomes will vary in different organisms 46 chromosomes in each cell for humans (23 pairs) 12 in housefly, 64 in horse… 9

GENES Humans have 23 pairs of chromosomes (46 total) 22 chromosome pairs + 1 sex chromosome pair (determines male or female) XX = female XY = male Exception: Sperm and egg cell each contain only 23 chromosomes (not 23 pairs) Zygote is made when sperm and egg combine (23 chromosomes from sperm + 23 chromosomes from egg = 46 total chromosomes) 10

PUNNETT SQUARES 11 Symbols represent the genes Gametes give 1 gene to a zygote Gametes = sperm and egg cells Mendel’s crosses Parent generation TT + tt F 1 generation Tt + Tt What are the genotypes and phenotypes?

VARIATIONS IN INHERITANCE Not all traits are dominant and recessive Incomplete Dominance Two traits combine to produce a different trait Both genes have same influence (no dominant or recessive trait expressed) Ex. red flower and white flower produce pink flower Codominance Dominant and recessive traits are both expressed 12

INCOMPLETE OR CODOMINANCE 13

PRACTICE A cross between purebred blue (B) and white (W) birds produces silver offspring. What are the genotypes of the parents? What are the genotypes of the offspring? What would be the phenotypic ratios/percentages of offspring produced by 2 silver birds? 14

PRACTICE Predict the phenotypic ratios of offspring when a homozygous white (WW) cow is crossed with a heterozygous roan (RW) bull. 15

PRACTICE What should the genotypes and phenotypes for cattle be if the cattle wanted to breed them and produce cattle with only red fur? 16

PRACTICE A cross between a black cat and a tan cat produces a tabby pattern (black and tan fur together) What type of inheritance? What percent of kittens would have tan fur if the tabby cat is crossed with a black cat? How many will have tabby fur? Black fur? 17

MULTIPLE GENE INHERITANCE Some traits are produced as a product of more than two genes Could be as many as 12 pairs of genes that control hair color 18

INHERITANCE OF SEX CHROMOSOMES The gender of the offspring is determined by the sex chromosome (23 rd pair) Each gamete (sperm or egg) will contain 1 chromosome from each pair of chromosomes ½ of sperm will contain X chromosome, ½ will contain Y chromosome The father’s sperm will determine the gender of the child 19

SEX-LINKED TRAITS Some inherited traits have genes located on the sex chromosomes (X + Y) Sex-linked traits Inherited trait that has a gene on the X chromosome, but not on the Y chromosome Since females have corresponding genes on both X chromosomes, the dominant trait will be shown Colorblindness is a sex-linked trait Trait given by symbol X G or X g 20

PEDIGREE Carrier People who have a gene for a trait but do not express the trait themselves Inherited Disorders Abnormal traits that are passed on through genes 21