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Biology Unit 8 Review: Heredity

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Presentation on theme: "Biology Unit 8 Review: Heredity"— Presentation transcript:

1 Biology Unit 8 Review: Heredity
The following includes the key terms and ideas for the major concepts we have covered this week concerning heredity. Use your worksheets and this PowerPoint to match terms to correct definitions and to answer questions related to the topic.

2 Heredity The passing of characteristics from parents to offspring is called heredity.

3 Heredity The study of heredity begin more than a century ago with the work of Gregor Mendel. Mendel carried out experiments in which he bred different varieties of garden peas. Mendel was the first to develop rules that accurately predicted patterns of heredity.

4 Heredity The patterns that Mendel discovered form the basis of genetics, the branch of biology that focuses on heredity.

5 Heredity Mendel’s initial experiments were monohybrid crosses. A monohybrid cross is a cross that involves one pair of contrasting traits. For example, crossing a plant with purple flowers with a plant with white flowers is a monohybrid cross.

6 Heredity Mendel carried out his experiments in three steps:
Mendel allowed each variety of garden pea to self-pollinate for several generations. This ensured that each variety was true-breeding for a particular character trait. For example, a true-breeding purple-flowering plant should produce only plants with purple flowers in following generations.

7 Heredity Mendel carried out his experiments in three steps:
Step 1: Thus these true breeding plants served as the parental generation in Mendel’s experiments. This parental generation, or P generation, are the first two individuals that are crossed in a breeding experiment.

8 Heredity Step 2: Mendel than cross-pollinated two P generation plants that had contrasting traits, such as purple flowers and white flowers. Mendel called the offspring of the P generation the first filial generation or F1 generation. He than examined each F1 plant and recorded the number of F1 plants showing each trait.

9 Heredity Step 3: Finally, Mendel allowed the F1 generation to self-pollinate. He called the offspring of the F1 generation plants the second filial generation or F2 generation.

10 Heredity Mendel also developed 4 hypothesis that make up the modern theory of “Mendelian theory of heredity” 1: For each inherited characteristic (trait) an individual has two copies of the gene; one from each parent.

11 Heredity 2: There are alternative versions of genes ( for example: the gene for a flower’s color can exist in a purple version or a white version) Today this different versions of a gene are called alleles.

12 Heredity 3: When two different alleles occur together, one may have no observable affect while the other may overpower and be visible. One trait dominates the other trait.

13 Heredity 4: The overpowering trait is called the dominant trait
the suppressed trait is the recessive trait.

14 Heredity If the two alleles of a particular gene present in an individual are the same (both BB or bb) the individual is said to be homozygous. If the alleles in an individual are different (Bb) than the individual is heterozygous

15 Heredity In a heterozygous individual (Bb) the dominant gene (B) will be the gene that overpowers the other and is visible. In the Bb combinations at right, the flower is purple because the B gene is the dominant gene.

16 Heredity The set of alleles that an individual has for a character is called it’s genotype. The genotype combinations at right are BB, Bb, Bb, and bb. The physical appearance of a character is called it’s phenotype. The purple flowers are the visible phenotype.

17 Heredity The phenotype is determined by which is the dominant trait present. In the genotypes at right; BB, Bb, and Bb, the B is dominant and determines the physical appearance.

18 Heredity Law 1: The Law of Segregation:
The first law of heredity, the law of segregation, states that the two alleles for a character segregate (separate) when gametes (sperm and egg cells) are formed.

19 Heredity Law 2: The Law of Independent Assortment:
States that the alleles of different genes separate independently of one another during gamete formation.

20 Heredity A Punnett Square is a diagram that predicts the outcome of a genetic cross by considering all possible permutations of the gene combinations for a trait when crossed.

21 Heredity The possible gametes that the other parent can donate are written across the other side, B and b. Remember, capital B represents a dominant trait while lowercase b represents a recessive trait.

22 Heredity When allele B is combined with the other allele B, the result is a genotype BB in the box on the Punnett square. Allele B and allele b combine to create genotype Bb in two of the grid boxes. Last, alleles b and b combine to create a genotype bb in the last grid box.

23 Heredity The figure at right shows the results of a hybrid cross between two pea plants that are both heterozygous (Bb) Since the B represents the dominant trait, any of the combinations with a B in it will result in a purple flower.

24 Heredity Probability is the likelihood that a specific event will occur. In the chart at right, the B is a dominant trait. Whenever the B is present in the crossbred genotype, the phenotype will be a purple flower. The ratio is 3 : 1 in favor of purple flowers. (3 purple for every 1 white) The probability is 3 out of 4 will be purple (the phenotype) or 75% probability of purple.

25 Heredity The probability of the genotype being homozygous (BB or bb) are 2 out of 4 or 50% The probability of the phenotype being heterozygous (Bb) is 2 out of 4 or 50% The probability of the flower being purple (phenotype) is 3 out of 4 or 75%

26 Heredity The probability of the genotype being homozygous (BB or bb) are 2 out of 4 or 50% The probability of the phenotype being heterozygous (Bb) is 2 out of 4 or 50% The probability of the flower being purple (phenotype) is 3 out of 4 or 75%

27 Heredity A pedigree is a chart of a family history that shows how a trait is present over generations in a family

28 Heredity In the pedigree below, we see a key to it’s right that explains what each symbol means in the pedigree. Like a map, the key is important to reading the pedigree.

29 Heredity The pedigree shows us who is male, female, who is married to whom else, and each couples direct children both male and female. In this pedigree we follow the path of a genetic disease passed through three generations.

30 Heredity In this pedigree we can also see which children in which generations have been affected by a disease that was genetically passed down.

31 Heredity We see the original carrier was Sue but in following generations the disease only showed up in male children of the family. In the pedigree below we see that the genetic disorder has affected only the males in the following generations. This indicates it is a sex-linked genetic disorder

32 Heredity If a gene is autosomal, it appears in both sexes equally.
If a gene is sex-linked however, it always appears only in one gender, usually males.


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