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Chapter 11: Introduction to Genetics. California content standards: Genetics 2c, d, g; 3a, b.
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Chapter 11: Introduction to Genetics California content standards: Genetics 2c, d, g; 3a, b
2c. Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete. 2d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).2g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents.
3a. Students know how to predict the probable outcome of phenotypes in a genetic cross from the genotypes of the parents and mode of inheritance (autosomal or X-linked, dominant or recessive). 3b. Students know the genetic basis for Mendel's laws of segregation and independent assortment.
11-1 Key Words • Genetics • Fertilization • True-breeding • Trait • Hybrid • Gene • Allele • Segregation • Gamete Quiz on these terms Thursday!
Intro Every living thing-plant or animal, microbe or human-has a set of characteristics inherited from its parents. 11-1
Definition • Genetics: the scientific study of heredity. 11-1
First clues to understanding how traits are inherited came from Gregor Mendel, an Austrian monk, in the mid 1800’s. His basic principles of heredity are still accepted today. 11-1
Unique because: 20,000 pea plants Used statistics Took detailed notes Mendel’s experiments: 11-1
Why peas? Flower structure Mendel knew that the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells. Mendel’s experiments:
During sexual reproduction, sperm and egg cells join in a process called fertilization. • Fertilization produces a new cell. 11-1
Why peas? Flower structure Presence of distinctive traits (wrinkled vs. smooth, color, etc.) Fast reproduction Mendel’s experiments: 11-1
Genes and DominanceA trait is a specific characteristic that varies from one individual to another. 11-1
Mendel’s work not recognized for 30 years (after his death). That’s just wrong! 11-1
Gregor Mendel’s Peas • Mendel had true-breeding pea plants that, if allowed to self-pollinate, would produce offspring identical to themselves. • Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants. • He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant. • These were the “P” generation. 11-1
Gregor Mendel’s Peas • This process is called cross-pollination. • Mendel was able to produce seeds that had two different parents. 11-1
Pure lines Seed produced 11-1
What did he do? Seed was produced. This seed was grown and called the first filial or “F1” generation. Mendel’s experiments: All plants were tall when grown. 11-1
hybrids F1 generation 11-1
Hybrid • The offspring of crosses between parents with different traits • Mendel’s F1 hybrid plants all had the character of only one of the parents. 11-1
Remember what a diploid organism is? Hybrid 1 “allele” from each parent Yy 11-1
Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. Today, scientists call the factors that determine traits genes. 11-1
Is that shortness trait lost forever? No baby, its only hidden.
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait. • The different forms of a gene are called alleles. 11-1
Mendel’s second conclusion is called the principle of dominance. • The principle of dominance states that some alleles are dominantand others are recessive. 11-1
An organism with a dominant allele for a trait will always exhibit that form of the trait. • An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present.
dominant 2 dominants dominant 1 dominant + 1 recessive 2 recessive recessive 11-1
What happens during segregation? • Segregation • Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation. • The traits controlled by recessive alleles reappeared in one fourth of the F2 plants. 11-1
Segregation • Mendel's F2 Generation F2Generation F1Generation PGeneration Tall Tall Tall Tall Short Tall Short Tall 11-1
Mendel assumed that a dominant allele had masked the corresponding recessive allele in the F1 generation. • The trait controlled by the recessive allele showed up in some of the F2 plants. 11-1
The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated, from the allele for tallness. • Mendel suggested that the alleles for tallness and shortness in the F1 plants segregated from each other during the formation of the sex cells, or gametes.
When each F1 plant flowers and produces gametes, the two alleles segregate from each other so thateach gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes—those with the allele for tallness, and those with the allele for shortness.
11-1 • Gametes are also known as • genes. • sex cells. • alleles. • hybrids.
11-1 • The offspring of crosses between parents with different traits are called • alleles. • hybrids. • gametes. • dominant.
11-1 In Mendel’s pea experiments, the male gametes are the • eggs. • seeds. • pollen. • sperm.
11-1 In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of • all short plants. • all tall plants. • half tall plants and half short plants. • all plants of intermediate height.
11-1 If a particular form of a trait is always present when the allele controlling it is present, then the allele must be • mixed. • recessive. • hybrid. • dominant.
Gene-Chromosome Theory 25-1 in “Bear Book”
Mendel concluded that forms of a trait must remain separate in offspring.Offspring receives 1 trait from each parent.Traits are coded for by genes. 25-1
Alleles • To agree with Mendel’s findings, each body cell should have 2 copies of each trait (alleles). • e.g. 2 copies of the gene for height 25-2
Alleles of 1 gene 25-2
Alleles Homozygous Dominant Gene 1 Gene 1 A A Homologous pair 25-2
Alleles Heterozygous Gene 1 Gene 1 A a Homologous pair 25-2
Alleles Homozygous recessive Gene 1 Gene 1 a a Homologous pair 25-2
