MADANIA (Lower Secondary)Grade 9 Biology Handout

INHERITANCE17 / 10 / 2011

 Name : ______________

Class : 9 ___

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Inheritance

• The transfer or transmission of some features from one generation to the next is called inheritance.

• The characteristics are controlled by genes which are like coded instruction.

• Genes from one generation are transmitted to the next in the gametes.

• At fertilization, the gametes fuse to form a zygote which contains the genetic information from both parents.

• A new individual grows from the zygote – half of its genetic information comes from its male parent and half from its female parent

• Mendel was the first scientist to develop a method for predicting the outcome of inheritance patterns.

• He performed his work with pea plants, studying seven traits: plant height, pod shape, pod color, seed shape, seed color, flower color, and flower location.

• Pea plants develop individuals that are homozygous for particular characteristics. These populations are known as pure lines.

Gregor Mendel: Father of Modern Genetics

Mitosis and meiosis

• Mitosis: type of nuclear division that occurs during growth and asexual reproduction

( somatic cell). The daughter cells are genetically identical.

• Meiosis: occurs in sex organs to form gametes. The daughter cells are not genetically identical.

MITOSIS MEIOSIS

PARENT CELL(before chromosome replication)

Site ofcrossing over

MEIOSIS I

PROPHASE ITetrad formedby synapsis of homologous chromosomes

PROPHASE

Duplicatedchromosome(two sister chromatids)

METAPHASE

Chromosomereplication

Chromosomereplication

2n = 4

ANAPHASETELOPHASE

Chromosomes align at the metaphase plate

Tetradsalign at themetaphase plate

METAPHASE I

ANAPHASE ITELOPHASE I

Sister chromatidsseparate duringanaphase

Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together

No further chromosomal replication; sister chromatids separate during anaphase II

2n 2n

Daughter cellsof mitosis

Daughter cells of meiosis II

MEIOSIS II

Daughtercells of

meiosis I

Haploidn = 2

n n n n

• Mendel was the first scientist to develop a method for predicting the outcome of inheritance patterns.

• He performed his work with pea plants, studying seven traits: plant height, pod shape, pod color, seed shape, seed color, flower color, and flower location.

• Pea plants develop individuals that are homozygous for particular characteristics. These populations are known as pure lines.

Gregor Mendel: Father of Modern Genetics

ILLUSTRATION

Mendelian crosses

• In his work, Mendel took pure-line pea plants and cross-pollinated them with other pure-line pea plants. He called these plants the parent generation.

• When Mendel crossed pure-line tall plants with pure-line short plants, he discovered that all the plants resulting from this cross were tall. He called this generation the F1 generation (first filial generation).

• Next, Mendel crossed the offspring of the F1 generation tall plants among themselves to produce a new generation called the F2 generation (second filial generation).

Two Innovations of Mendel

1. Developed pure lines

2. Counted his results and kept statistical notes

• Pure Line (galur murni) - a population that breeds true for a particular trait

Mendelian crosses

• To predict the possibility of an individual trait, several steps are followed:

1. The dominant allele is represented by a capital letter while the recessive allele by the corresponding lowercase letter. Homozygous dominant individual (the genotype is EE); heterozygous individual (the genotype is Ee); and for a homozygous recessive person (the genotype is ee).

2. Performing a genetic cross is determining the genotypes of the parents and the genotype of the gametes. A heterozygous male and a heterozygous female to be crossed have the genotypes of Ee and Ee. During meiosis, the allele pairs separate. A sperm cell contains either an E or an e, while the egg cell also contains either an E or an e.

Mendelian crosses

3. To continue the genetics problem, a Punnett square is used. A Punnett square is a boxed figure used to determine the probability of genotypes and phenotypes in the offspring of a genetic cross.

4. This is done by filling in each square with the alleles above it and at its left.

5. Therefore, the ratio of phenotypes is 3 with curly hair to 1 with straight hair (3:1). The ratio of genotypes is 1:2:1 (1 EE : 2 Ee : 1 ee).

Monohybrid cross• Involves a study of inheritance patterns for organisms

differing in one traits. • Using symbols we can predict the cross of tall (DD) and

short (dd) pea plants in the following manner:

Dihybrid Cross Problem Set • A dihybrid cross involves a study of inheritance patterns

for organisms differing in two traits. • Mendel invented the dihybrid cross to determine if

different traits of pea plants, such as flower color and seed shape, were inherited independently.

Terms to know in Mendelian Genetics

1. Alleles: The different forms of a gene. Y and y are different alleles of the gene that determines seed color. Alleles occupy the same locus, or position, on chromosomes.

2. F1 generation Offspring of a cross between true breeding plants, homozygous for the trait of interest

3. F2 generation Offspring of a cross involving the F1 generation.

4. Homozygote - an individual which contains only one allele at the allelic pair; for example DD is homozygous dominant and dd is homozygous recessive; pure lines are homozygous for the gene of interest

5. Heterozygote - an individual which contains one of each member of the gene pair; for example the Dd heterozygote

6. Incomplete dominance

The flowers of the snapdragon plant can be red, pink, or white. The genotype RR results in red flowers and rr results in white flowers. The heterozygote genotype of Rr results in pink flowers.

7. Genotype - the specific allelic combination for a certain gene or set of genes based on trait.

8. Monohybrid cross. Cross involving parents differing in only one trait.

Terms to know in Mendelian Genetics

Terms to know in Mendelian Genetics

9. Phenotype The physical appearance of an organism with respect to a trait, i.e. yellow (Y) or green (y) seeds in garden peas. The dominant trait is normally represented with a capital letter, and the recessive trait with the same lower case letter.

10. Recessive trait. The opposite of dominant. A trait that is preferentially masked.

11. Dominance - the ability of one allele to express its phenotype (trait)

Terms to know in Mendelian Genetics

12. Backcross - the cross of an F1 hybrid to one of the homozygous parents; for pea plant height the cross would be Dd x DD or Dd x dd; most often, though a backcross is a cross to a fully recessive parent

13. Testcross - the cross of any individual to a homozygous recessive parent; used to determine if the individual is homozygous dominant or heterozygous

14. Monohybrid cross - a cross between parents that differ at a single gene pair (usually AA x aa)

15. Monohybrid - the offspring of two parents that are homozygous for alternate alleles of a gene pair

EXERCISES-1

1.Human blood type is determined by codominant alleles. There are three different alleles, known as IA, IB, and i. The IA and IB alleles are co-dominant, and the i allele is recessive. The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, respectively). A woman with type A blood and a man with type B blood could potentially have offspring with which of the following blood types? A. type A B. type B C. type AB D. type O E. all of the above

• What are the possible blood types of the offspring of a cross between individuals that are type AB and type O? (Hint: blood type O is recessive)

A. AB or O B. A, B, or O C. A or B D. A, B, AB, or O E. A, B, or AB

EXERCISES-2

• A pea plant is heterozygous for both seed shape and seed color. S is the allele for the dominant, spherical shape characteristic; s is the allele for the recessive, dented shape characteristic. Y is the allele for the dominant, yellow color characteristic; y is the allele for the recessive, green color characteristic. What will be the distribution of these two alleles in this plant's gametes?

A. 50% of gametes are Sy; 50% of gametes are sY B.

25% of gametes are SY; 25% of gametes are Sy;25% of gametes are sY; 25% of gametes are sy.

C. 50% of gametes are sy; 50% of gametes are SYD. 100% of the gametes are SsYy E. 50% of gametes are SsYy; 50% of gametes are SSYY.

EXERCISES-3

• Which of the following genetic crosses would be predicted to give a phenotypic ratio of 9:3:3:1?

A. SSYY x ssyy

B. SsYY x SSYy

C. SsYy x SsYy

D. SSyy x ssYY

EXERCISES-4

• The gametes of a plant of genotype SsYy should have the genotypes:

A. Ss and Yy

B. SY and sy

C. SY, Sy, sY, and sy

D. Ss, Yy, SY and sy

E. SS, ss, YY, and yy

EXERCISES-5

Monohybrid inheritance

• It concerns the inheritance of a single characteristic, such as plant height or flower color

• There are three possible genotypes for plant height:

1.TT = homozygous tall

2.Tt = heterozygous tall

3. tt = homozygous dwarf

Monohybrid inheritance

• Crossing a homozygous tall plant with a homozygous dwarf plant