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Introduction to Genetics – Part 1. Genetics – Study of heredity is often divided into four major subdisciplines : 1. Transmission genetics, deals with the transmission of genes from generation to generation 2. Molecular genetics deals with the structure

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introduction to genetics part 1

Introduction to Genetics – Part 1

Genetics – Study of heredity is often divided into four major subdisciplines:

1. Transmission genetics, deals with the

transmission of genes from generation to


2. Molecular genetics deals with the structure

and function of genes at the molecular level

3. Population genetics, which deals with heredity in

groups of individuals for traits determined by one

or only a few genes

4. Quantitative genetics, deals with the heredity of

traits in groups of individuals where the traits are

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

and carrying information (alleles) for the same

traits (Fig. 11-14)

diploid vs haploid

Diploid vs Haploid

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?

phases of meiosis

Phases of Meiosis

During meiosis the chromosomes replicate once, but the cell divides twice – Fig. 11-15

Meiosis results in two haploid daughter cells with half the number of chromosomes as the original cell

phases of meiosis1

Phases of Meiosis

Prophase I

Homologous chromosomes pair (synapsis) to

form a tetrad

phases of meiosis2

Phases of Meiosis

Prophase I

Crossing over –

exchange of segments

between nonsister


**increases genetic


phases of meiosis3

Phases of Meiosis

Metaphase I

Tetrads line up on equatorial plane

phases of meiosis4

Phases of Meiosis

Anaphase I

Disjunction occurs - homologous chromosomes

from each tetrad separate

Cytokinesis begins during late anaphase/early


phases of meiosis5

Phases of Meiosis

Telophase I

End of first meiotic division

phases of meiosis7

Phases of Meiosis

Metaphase II

phases of meiosis9

Phases of Meiosis

Telophase II

phases of meiosis10

Phases of Meiosis


meiosis quizzes

Meiosis Quizzes


introduction to genetics part 2

Introduction to Genetics – Part 2

Gregor Mendel – “father” of modern genetics

introduction to genetics part 21

Introduction to Genetics – Part 2

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

introduction to genetics part 22

Pea plants are:

- easy to grow

- matured quickly

- show contrasting


- control pollination

Introduction to Genetics – Part 2

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

genes and dominance

Genes and Dominance

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

genes and dominance2

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

Homozygous – having two identical


TT – homozygous dominant

tt - homozygous recessive

Heterozygous – having two different

forms of a gene - Tt

Genes and Dominance

genes and dominance4

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

Genes and Dominance

probability punnett squares

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

Probability & Punnett Squares

probability punnett squares1

Punnett Square – a diagram used to show the results of a cross – Fig. 11-7

Phenotype – physical trait that appears as a result of genetic makeup

Probability & Punnett Squares

Genotype – the genetic makeup of an organism; total set of genes

exploring mendelian genetics

Principle of Independent Assortment – Genes for different traits can segregate independently during the formation of gametes. (Fig. 11-9, 11-10)

Exploring Mendelian Genetics

exploring mendelian genetics1

Incomplete Dominance – both alleles contribute to the phenotype and neither is dominant over the other – Fig. 11-11

Exploring Mendelian Genetics

exploring mendelian genetics2

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

Exploring Mendelian Genetics

linkage and gene maps

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. 11-19)

Linkage and Gene Maps

linkage and gene maps1

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

Linkage and Gene Maps

links to practice punnett squares

Links to Practice Punnett Squares