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Chapter 2

CH.2 Heredity.docx


Department
Psychology
Course Code
PSYB32H3
Professor
Mark Phortney
Chapter
2

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Twinkle Arora (PSYB20)
1
CHAPTER 2: HEREDITY AND THE ENVIORNMENT
- Genotype the particular set of genes that a person inherits from her parents
- With the exception of identical twins, no two people have exactly the same genotypes
- Genotype interacts with the environment to produce the phenotype
- Phenotype created by the interaction of a person`s genotype or genetic makeup, with the
environment; the visible expression of the person’s particular physical and behavioural
characterises
- Examples of the phenotype intellectual skills, motor abilities and personality traits
- Genetic transmission in a female`s oviduct the sperm and the egg (male and female gametes
reproductive cells) unite to create a zygote
- Ovum the female germ cell, or egg
- Sperm the male germ cell , the smallest of all human cells is the shape of a head
- After 9 months baby 7 to 8 pounds and are about 50 cm long
- Chromosomes and genes are located inside the nucleus or centre of the cell
- 23 chromosome pairs 46 in total
- Chromosomes threadlike structures that carry genetic information to help direct environment
- Each pair is homologous similar in shape and function to one of the chromosomes
- These chromosomes are passed on to every cell in a person`s body with the exception of the
reproductive cells
- Meiosis - reproductive cells divide to produce new germ cells with half the normal complement of
chromosomes ; thus male and female germ cells (sperm and egg) each contain only 23
chromosomes so that when they unite, the new organism they form will have 46 chromosomes,
half from each parent
- Crossing over the process by which equivalent sections of homologous chromosomes switch
places randomly, shuffling the genetic information each carries
- Mitosis the process in which a body cell divides in two, first duplicating its chromosomes so that
the new daughter cells contain the usual 46 chromosomes
- Autosomes the 22 paired non sex chromosomes

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Twinkle Arora (PSYB20)
2
- Deoxyribonucleic acid (DNA) - a ladder like molecule that stores genetic information in cells and
transmits it during reproduction
- DNA is made out of nucleotides that are held together by 2 parallel strands
- Nucleotide a compound containing a nitrogen base, a simple sugar and a phosphate group
- BASES - ADENINE and THYMINE Bind together
- BASES CYTOSINE and GUANINE Bind together
- Portions of the chromosome’s DNA molecule called genes are located at particular sites on the
chromosome where they code for the production of certain kinds of protein
- Proteins are fundamental components of all living cells, and are any of a group of complex
organic molecules containing O2 , C2, N, H2 and S composed of amino acids
- The genetic code is written in the order in which the 4 bases are included in the gene, the DNA
then splits down the middle so that its pairs of bases are no longer joined and the bases bond w.
other free nucleotides
- Gregor Mendel spent years cross breeding pea plants he observed traits of the plants varied
from one generation to another with a trait that had been present in one generation disappearing
in the next generation but then repapering again in the following generations
- he came up with principals principle of segregation and then principal of independent assortment
- principle of segregation states that each inherited trait comes from one’s parent as a separate
unit (e.g. flower colour, stem height etc)
- principal of independent assortment states that inheritance that the inheritance of various traits
occurs independently of one another
- allele an alternative forms of a gene, typically a gene has 2 alleles, one inherited from the
individual’s mother and one from the other
- homozygous two of the same alleles
- heterozygous two different alleles
- co-dominance a genetic pattern in which heterozygous alleles for a particular trait for which they
code simultaneously and with equal force
- dominant describing the more powerful of two alleles in a heterozygous combination
- recessive - describing the weaker of two alleles in a heterozygous combination
- societies prohibit marriage among close blood relations because of harmful recessive genes
- sex chromosomes in both males and females, the 23rd pair of chromosomes which determine
the individuals gender and are responsible for sex-related characteristics ; in females( XX)
chromosomes and in males (XY)
- Chromosome X comes from the child’s mother and Chromosome Y comes from the father
- Chromosome X is five times longer than chromosome Y thus carries more genes
- X linked gene genes that are carried on the X chromosome and that may have no analogous
genes on the Y chromosome in males
- Hemophilia- a disorder caused by an X linked recessive gene in which the blood fails to clot; found
more often in males than females
- The allele for haemophilia is recessive, a female who inherits it will normally clot blood as long as
her second allele inherited from her other parent does NOT code for haemophilia. Only if she is
homozygous for the recessive allele will her blood clotting be impaired
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