Genetics – Study of heredity is often divided into four major subdisciplines: 1. Transmission genetics, deals with the transmission of genes from generation to transmission of genes from generation to generation generation 2. Molecular genetics deals with the structure 2. Molecular genetics deals with the structure and function of genes at the molecular level and function of genes at the molecular level 3. Population genetics, which deals with heredity in 3. Population genetics, which deals with heredity in groups of individuals for traits determined by one groups of individuals for traits determined by one or only a few genes or only a few genes 4. Quantitative genetics, deals with the heredity of 4. Quantitative genetics, deals with the heredity of traits in groups of individuals where the traits are traits in groups of individuals where the traits are determined by many genes simultaneously determined by many genes simultaneously

Cell division in diploid cells that results in haploid cells; reduction division Homologous chromosomes – a pair of chromosomes having the same size and shape chromosomes having the same size and shape and carrying information (alleles) for the same and carrying information (alleles) for the same traits (Fig ) traits (Fig )

Diploid – having two sets of chromosomes, or all the homologous chromosomes that are characteristic of the species ( 2n ) Haploid – having only one chromosome from each pair of homologous chromosomes (n) How does a cell go from diploid to haploid?

During meiosis the chromosomes replicate once, but the cell divides twice – Fig Meiosis results in two haploid daughter cells with half the number of chromosomes as the original cell

Prophase I Homologous chromosomes pair (synapsis) to form a tetrad form a tetrad

Prophase I Crossing over – exchange of segments exchange of segments between nonsister between nonsister chromatids; chromatids; **increases genetic **increases genetic variation** variation**

Metaphase I Tetrads line up on equatorial plane

Anaphase I Disjunction occurs - homologous chromosomes from each tetrad separate from each tetrad separate Cytokinesis begins during late anaphase/early Cytokinesis begins during late anaphase/early telophase telophase

Telophase I End of first meiotic division coach/meiosis/mei1ani.html coach/meiosis/mei1ani.html

Prophase II

Metaphase II

Anaphase II

Telophase II coach/meiosis/mei2ani.html coach/meiosis/mei2ani.html

Overview m/meiosis.html m/meiosis.html

h/meiosis/quiz.html iz/mitosis.htm THIS SLIDE ENDS PART ONE

Gregor Mendel – “father” of modern genetics

Fertilization – the union of a female and male gamete (specialized sex cell formed during meiosis)

Pea plants are: - easy to grow - easy to grow - matured quickly - matured quickly - show contrasting - show contrasting traits traits - control pollination - control pollination True breeding – pure for a particular trait. If plants with yellow seeds were self pollinated for several generations they would always produce plants with yellow seeds

Gene – a distinct unit of hereditary material found in chromosomes; a sequence of nucleotides in DNA

Allele – the different forms of the gene for a trait

Principle of Dominance states that some alleles are dominant and others are recessive Homozygous – having two identical alleles alleles TT – homozygous dominant tt - homozygous recessive Heterozygous – having two different forms of a gene - Tt forms of a gene - Tt

Principle of Dominance states that some alleles are dominant and others are recessive

Principle of Segregation – factors that occur in pairs are separated from each other during gamete formation and recombined at fertilization ( Fig. – 11-5)

Probability – likelihood that a particular event will occur Principle of Probability – if there are several possible event that might happen, and no one of them is more likely to happen than any other, then they will happen in equal numbers over a large number of trials Example – Coin Toss – Fig. 11-7

Punnett Square – a diagram used to show the results of a cross – Fig Phenotype – physical trait that appears as a result of genetic makeup Genotype – the genetic makeup of an organism; total set of genes

Principle of Independent Assortment – Genes for different traits can segregate independently during the formation of gametes. (Fig. 11-9, 11-10) m/thelifewire/content/c hp10/ html m/thelifewire/content/c hp10/ html

Incomplete Dominance – both alleles contribute to the phenotype and neither is dominant over the other – Fig

Co-Dominance – Two dominant alleles are expressed at the same time Multiple Alleles – 3 or more different alleles of a gene; each combination producing a different phenotype

Polygenic Traits – traits controlled by two or more genes; genes may or may not be on the same chromosome

Genetics and the Environment – environmental factors can influence “genetic potential”

Genes located on the same chromosome tend to be inherited together in genetic crosses because the chromosome is passed along as a unit. Such genes are said to be linked genes. (Fig )

Gene Map – an ordered list of the genes along a particular chromosome. The farther apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency. The distance between genes is expressed in “map units” and is defined as equivalent to a 1% recombination frequency

htm htm htm htm