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Transcript
Unit 7:Introduction to Genetics Test on: Intro Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of heredity which is the set of characteristics we _______, our parents receive from __________. The study of genetics heredity is known as ________. I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278) In sexual reproduction, an egg and sperm cell fuse together to create a zygote fertilized egg or ________. Egg and gametes sperm cells are known as _________. Gametes are the only cells in the body that are not produced by mitosis ________. I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278) Instead gametes are created through a special process of cell division called meiosis __________ which halves the chromosome _______ number. Meiosis only ovaries occurs in the _________ of females and the testes of males. ________ A. Chromosome Number 1. Human _______ somatic cells, or body cells, contain ___ 46 chromosomes. Somatic cells 2n because these cells are ________ or ___ diploid double set of chromosomes – contain a ______ half (___) and half (___) 23 from ______ mom 23 from ____. These “matching” dad chromosomes are known as _______________. A homologous pair homologous pairs is a pair of chromosomes – one from each type of traits parent, with the same ___________ or _______. genes A. Chromosome Number egg and ______) sperm 2. Human gametes (____ 23 chromosomes. They are contain ____ haploid or __. ______ n These cells contain ___ 1/2 the single total number of chromosomes, a _______ set of chromosomes. When the gametes fuse together in ___________, fertilization the zygote has _______ 46 resulting ________ chromosomes. B. Formation of Gametes: Meiosis Gametes are formed in meiosis – a special type of cell division that only occurs in the _______ ovaries of females and ______ testes of males. In meiosis, DNA is replicated once in ___________________, S phase of the cell cycle but the cell goes through two cell divisions, resulting in ___ 4 1/2 cells with _______ the original chromosome number. Meiosis occurs in two stages: 1. Meiosis I Prior to meiosis I, the DNA is replicated in S____________________________. phase of the cell cycle (or interphase) When the chromosomes, each consisting of 2 _______________ sister chromatids line up in the middle of the cell in __________ metaphase I, they homologous pairs. In anaphase line up in ___________ I and telophase I, the homologous pairs __________, but the sister chromatids and separate centromeres are still intact. _____________ Meiosis occurs in two stages: 1. Meiosis I Two cells are formed, each with 23 pairs of _______________ ___ sister chromatids making up ___ 23 chromosomes, but there are no longer any ________________ homologous pairs present, so the two cells are ____________. haploid or n Meiosis occurs in two stages: 2. Meiosis II The process continues with the two cells formed moving directly into prophase II without any further ________________. replication of DNA After the chromosomes align in the middle of the cell in __________ metaphase II, this time the sister chromatids are pulled apart in anaphase II. _________ Meiosis occurs in two stages: 2. Meiosis II Two new cells are formed from each of the two cells formed in Meiosis I, resulting in a total of 4 new cells, each with ___the ___ 1/2 original number of chromosomes. The cells produced are called gametes _______. Therefore, meiosis results in 4 haploid gametes C. Crossing Over Crossing over occurs during prophase I homologous ___________ when ___________ pairs of chromosomes come together. sister chromatid A portion of one ______________ may be broken off and exchanged with the corresponding portion of a sister chromatid of the homologous chromosome. Crossing over is very increases the genetic common and __________ variability in offspring. II. HISTORY OF GENETICS (pp. 263-270) A. Gregor Mendel Genetics Mendel Known as the “Father of ________”, pea is famous for his experiments with ____ plants. He used true-breeding pea plants, purebred, pureline and which means _______________ characteristics always show. This generation of true-breeding plants is known P generation. Mendel studied seven as __ traits ____, including plant height, seed color, flower color, etc. II. HISTORY OF GENETICS (pp. 263-270) A. Gregor Mendel A trait is an _______________. inherited characteristic Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg same plant. Mendel from _____ controlled the fertilization process of the pea plants by self-pollination preventing ______________ and controlling cross-pollination II. HISTORY OF GENETICS (pp. 263-270) B. Mendels’ Results • 1. P generation – Crossed pureline plants with one trait _________ pureline plants with the with ________ other. For example, tall plants X short plants _____________________ II. HISTORY OF GENETICS (pp. 263-270) B. Mendels’ Results 2. F1 generation – Offspring produced from _____. P x P In F1, one trait seemed to disappear ________. For example, tall plants X short plants = ___________. all tall plants 3. F2 generation – Offspring produced F1 x F1 from _______. In F2, trait that disappeared in F1 reappeared in ____ 1/4 of the offspring; the other ¾ showed trait seen in F1 ______________. II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles After analyzing his results carefully, Mendel formed conclusions that increased understanding of inheritance and opened the door for the study of genetics. genes determine 1. Individual units called _______ inheritable characteristics. A gene is a DNA that codes for a specific portion of _____ trait ______. II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles 2. For each gene, an organism inherits two alleles, one from each parent Alleles are _______. different forms or gene _____________ possibilities of a ______. a. If the two alleles are the same, the organism is said to homozygous for that be ____________ trait and the allele will be expressed. II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles b. If the two alleles differ, the organism is said to be __________ heterozygous for that trait and only one allele will be expressed. The expressed allele is the ________ dominant allele, designated by an _____-case letter. The upper allele that is not expressed in a recessive heterozygous trait is ________, designated by a _____-case letter. A lower recessive allele is only expressed when an homozygous for that allele organism is ___________________. II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles 3. In meiosis, the two alleles for a separate Each trait segregate (_______). egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. Due to the random separation of chromosomes in meiosis, there is a 50% chance that a copy of that ____ allele will end up in the gamete produced. This is known as the principle of segregation. II. HISTORY OF GENETICS (pp. 263-270) D. Genetics Terminology Physical description of trait; for 1. Phenotype - ________ example, ______________ tall, short 2. Genotype – Genetic make-up of an organism TT, Tt, tt or set of alleles; for example, ____________ 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, R and wrinkled is round is designated __ designated __. r II. HISTORY OF GENETICS (pp. 263-270) D. Genetics Terminology a. Homozygous dominant for pea seed shape is RR Seed shape? ______ round written ____. RR Phenotype = ______ round Genotype = ___; b. Heterozygous for pea seed shape is written ____. Seed shape? _______ round Rr Rr Phenotype = ______ round Genotype = ___; c. Homozygous recessive for pea seed shape is written __. rr Seed shape? _________ wrinkled Genotype = ___; rr Phenotype = _________ wrinkled III. ANALYZING INHERITANCE (pp.135-137) A. Probability Due to the law of segregation, if you know the genotype of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up heads after being flipped is (fraction) 1/2 (ratio) ________, 1:2 _____, or (percent) _______. 50% III. ANALYZING INHERITANCE (pp.135-137) B. Punnett Squares A Punnett square is a tool used to predict meiosis and the possible outcomes of ________ fertilization in other words, a Punnett ___________; square is used to determine the probability of certain traits appearing in offspring.