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Heredity – The passing of characteristics from

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Presentation on theme: "Heredity – The passing of characteristics from"— Presentation transcript:

1 In this family portrait, are the grandparents the parents to the mother or father? How can you tell?

2 Heredity – The passing of characteristics from
parent to offspring. Genetics – the study of heredity

3 Gregor Mendel (1822-1884) The father of genetics.

4 The Role of Fertilization
During sexual reproduction, male and female reproductive cells join in a process known as fertilization to produce a new cell. In peas, this new cell develops into a tiny embryo encased within a seed.

5 The Role of Fertilization
Self fertilization creates offspring with identical traits to themselves. Mendel called these plants true breeding. In other words, the traits of each successive generation would be the same.

6 Who is the father of Genetics?
Gregor Mendel

7 A trait is a specific characteristic of an individual, such as seed color or plant height, and may vary from one individual to another.

8 The Role of Fertilization
Mendel studied seven different traits of pea plants, each of which had two contrasting characteristics, such as green seed color or yellow seed color. Mendel crossed plants with each of the seven contrasting characteristics and then studied their offspring. The offspring of crosses between parents with different traits are called hybrids.

9 Genes and Alleles When doing genetic crosses, we call the original pair of plants the P, or parental, generation. Their offspring are called the F1, or “first filial,” generation. In each cross, the nature of the other parent, with regard to each trait, seemed to have disappeared.

10 Genes and Alleles From these results, Mendel drew two conclusions. His first conclusion formed the basis of our current understanding of inheritance. An individual’s characteristics are determined by factors that are passed from one parental generation to the next. Scientists call the factors that are passed from parent to offspring genes.

11 Genes and Alleles Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting varieties. These gene variations produced different expressions, or forms, of each trait. The different forms of a gene are called alleles.

12 What are the genes? What are the alleles for each gene?

13 Dominant and Recessive Traits
Mendel’s second conclusion is called the principle of dominance. This principle states that some alleles are dominant and others are recessive. An organism with at least one dominant allele for a particular form of a trait will exhibit that form of the trait. An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele for the trait is not present.

14 Which allele is dominant for each of the genes?

15 P F1

16 F1 F2 Mendel found in the F2 generation that about ¼ of the plants displayed the recessive allele for the trait.

17 Yy Gene – pea color Alleles – yellow green Dominant (Y) Recessive (y)
Mendel realized that there were two alleles for this trait – yellow and green peas. He also discovered one was dominant over the other – which one? The pea plants in Mendel’s F1 generation had both alleles Mendel suggested that during the formation of sex cell’s, or gametes, these alleles seperated, or segregated from each other Yy Y y

18 Definitions Segregation – seperation Gametes – sex cells
During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene.

19 Name one gene(trait) that you inherited from your parents
Name one gene(trait) that you inherited from your parents. What are the possible alleles for this trait.

20 How do scientist express alleles?
With letter abbreviations, Capital letter for dominant allele Lower case letter for recessive allele

21 Allele representation
G – green (dominant) g – yellow (recessive)

22 genotype The alleles that are present in the organism for the specific gene.(The genetic make up) GG or Gg or gg

23 phenotype The trait that is expressed (what we see)

24 What is the phenotype? What are the possible genotypes?

25 homozygous When an organism has two identical alleles for a particular gene GG gg

26 heterozygous When an organism has two different alleles for the same gene. Gg

27 What are the 4 possible allele combinations for the gametes of a parent who has the following genotype: BbGg

28 BbGg Bb BG bG bg

29 According to what we learned in the past week, what would you predict the offspring to look like?
This cross is an exception to Mendel’s principle. It is displaying Incomplete Dominance Incomplete Dominance – when some alleles are neither dominant or recessive. The heterozygous phenotype expresses itself somewhere between the 2 homozygous phenotypes.

30 Codominance When the cross produces an offspring in which both alleles are clearly expressed.

31 Multiple Alleles A gene with more than 2 alleles.
An individual will only have 2 of the alleles, however there are many different alleles within the population

32 Polygenic traits Traits produced by the expression of several genes.

33 Genes and the Environment
Environmental conditions can affect gene expression and influence genetically determined traits. Butterflies that hatch in summer have different color patterns on wings than those hatching in the spring. -shorter days more pigment in their wings (pigment helps to warm up butterfly)

34 What is the difference between a monohybrid cross and a dihybrid cross?

35 Monohybrid is a cross that looks at only one trait
Dihybrid is a cross that is looking at two traits.

36 Which is the genotype found in a regular cell in parent
Which is the genotype found in a regular cell in parent? Which is the genotype found in a gamete produced by parent? A. RrGg B. RG


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